You finally upgraded to a king size bed frame. More space, no more elbowing your partner at 3am, room to actually stretch out. But now you’re lying on the old double mattress you shoved onto it as a temporary fix, and it looks ridiculous — a small rectangle floating in the middle of a bigger rectangle. Time to sort it properly.
Finding the right king size mattress in the UK is harder than it should be. Every brand claims to be the best, the price range runs from £300 to £3,000, and half the mattresses you can’t even try before buying. After testing, researching, and comparing every major king size option available to UK buyers, here are the ones actually worth your money.
In This Article
- Best Overall King Size Mattress
- What Size Is a UK King Mattress?
- How to Choose a King Size Mattress
- Best King Size Mattresses Compared
- Emma Original King Mattress
- Simba Hybrid Pro King Mattress
- Hypnos Orthos Support King Mattress
- Silentnight Mirapocket 1200 King
- Brook + Wilde Lux King Mattress
- Nectar Memory Foam King Mattress
- Head to Head: Which King Mattress Should You Buy?
- King Size Mattress Buying Mistakes to Avoid
- Where to Buy King Size Mattresses in the UK
- Bottom Line
- Frequently Asked Questions
Best Overall King Size Mattress
If you want the short answer: the Emma Original is the best king size mattress for most people in the UK. It’s around £550-650 depending on sales (and Emma runs sales constantly), offers excellent support across all sleeping positions, and comes with a 200-night trial so you can actually live with it before committing. It’s the one we’d recommend to anyone who doesn’t have very specific requirements.
But “best overall” doesn’t mean best for everyone. If you sleep hot, prefer pocket springs over foam, or have a bigger budget, keep reading — there’s a better pick for you further down.
What Size Is a UK King Mattress?
Before spending a penny, know your measurements. A UK king size mattress measures 150 × 200 cm (5 feet × 6 feet 6 inches). This is different from a European king (160 × 200 cm) and very different from a US king (193 × 203 cm).
Why does this matter? Because if you’re buying online from an international brand, you need to make sure you’re getting the UK king, not the European version. The 10cm width difference is enough to leave a visible gap in your bed frame — or worse, a mattress that doesn’t fit at all.
Our complete guide to UK mattress sizes covers every UK size including super king if you’re not sure what fits your room.
Is a King Size Right for Your Room?
A king mattress needs a bedroom that’s at least 3.6 × 3.6 metres to avoid feeling cramped. You need 60cm clearance on both sides for getting in and out, plus space at the foot for a chest of drawers or wardrobe access.
In a typical UK three-bed semi, the master bedroom usually accommodates a king with room to spare. In a two-bed flat or a Victorian terraced house, measure first — those rooms can be deceptively narrow.
How to Choose a King Size Mattress
The mattress industry loves overcomplicating this. There are really only five things that matter:
Mattress Type
- Memory foam: Contours to your body shape, good pressure relief, tends to sleep warmer. Best for side sleepers and people with joint pain.
- Pocket sprung: Individual springs in fabric pockets, responsive bounce, better airflow. Best for couples (less motion transfer with 1,000+ springs) and people who sleep hot.
- Hybrid: Combines springs and foam layers. The current sweet spot for most people — you get support from the springs and comfort from the foam.
- Latex: Bouncy, cool-sleeping, durable. More expensive and harder to find in the UK.
Firmness Level
Firmness is personal, but as a rough guide:
- Side sleepers: Medium to medium-soft. Your shoulders and hips need to sink in.
- Back sleepers: Medium to medium-firm. Support across the spine without arching.
- Front sleepers: Firm. Stops your hips dropping and straining your lower back.
- Couples with different preferences: Look for dual-tension options or a medium-firm hybrid that works as a compromise.
Support and Pressure Relief
These are not the same thing. Support keeps your spine aligned. Pressure relief stops your shoulders and hips aching. A mattress can be supportive but still create pressure points (old-school pocket sprung). The best modern mattresses do both — zoned support with softer comfort layers on top.
Temperature Regulation
Memory foam sleeps warm. If you or your partner runs hot at night, this matters. Look for gel-infused foam, open-cell structures, or spring-based mattresses that allow more airflow. The NHS acknowledges that bedroom temperature affects sleep quality — the ideal range is 16-20°C, and a hot mattress works against you.
Trial Period and Returns
Every mattress-in-a-box brand offers a trial — typically 100-200 nights. This matters more than any review, including this one. Your body needs 2-4 weeks to adjust to a new mattress, so a 30-day trial isn’t really enough. Look for 100 nights minimum.
For more on what to prioritise, our complete mattress buying guide covers every factor in detail.
Best King Size Mattresses Compared
Here’s how the six best king size mattresses available in the UK stack up:
- Emma Original — Best overall, £550-650, memory foam, 200-night trial
- Simba Hybrid Pro — Best hybrid, £800-950, pocket springs + foam, 200-night trial
- Hypnos Orthos Support — Best for back pain, £1,200-1,400, pocket sprung, no trial (try in John Lewis)
- Silentnight Mirapocket 1200 — Best budget option, £350-450, pocket sprung, 60-night trial
- Brook + Wilde Lux — Best for side sleepers, £750-900, hybrid, 200-night trial
- Nectar Memory Foam — Best value foam, £450-550, memory foam, 365-night trial
Emma Original King Mattress
Price: ~£550-650 (frequently discounted to ~£400-450 during sales) Type: Memory foam Trial: 200 nights Warranty: 10 years
The Emma Original has been the UK’s best-selling mattress-in-a-box for good reason. The three foam layers — a breathable top layer, pressure-relieving memory foam, and a supportive base — work together to create a mattress that suits the widest range of sleepers.
What We Like
- Pressure relief is excellent. Side sleepers especially benefit — shoulders and hips sink in without bottoming out.
- Motion isolation is superb. Your partner can get up for a glass of water at 2am and you won’t feel a thing.
- The cover is removable and washable. Small detail, huge difference for allergies and general hygiene.
- 200-night trial with free returns. Emma collects the mattress if you don’t like it. No hassle.
What Could Be Better
- Sleeps warmer than springs. The top layer helps, but if you naturally run hot, you’ll notice — especially in summer.
- Edge support is average. Sitting on the edge feels like you’re sliding off. Fine for sleeping, noticeable for perching.
- Not available to try in store. Online only, which makes the 200-night trial essential.
Who It’s For
Couples who want excellent motion isolation. Side sleepers who need pressure relief. Anyone who wants a reliable, well-reviewed mattress without overthinking it.
Simba Hybrid Pro King Mattress
Price: ~£800-950 (often on sale around £600-700) Type: Hybrid (titanium Aerocoil springs + foam) Trial: 200 nights Warranty: 10 years
Simba’s Hybrid Pro layers their proprietary Aerocoil springs between foam layers, creating a mattress that bounces like a spring but cushions like foam. It’s the best of both worlds, and it sleeps cooler than any pure foam option.
What We Like
- Sleeps noticeably cooler than the Emma Original or Nectar. The spring layer creates airflow channels that foam alone can’t match.
- Responsive and bouncy. If you don’t like that “sinking into quicksand” feeling of memory foam, this is a much better experience.
- Excellent edge support. You can sit on the edge without feeling like you’re about to roll off — useful if you sit on the bed to put shoes on.
- Zoned support with firmer springs under the lower back and softer under shoulders.
What Could Be Better
- More motion transfer than the Emma. The springs add responsiveness but also transmit more movement. Light sleepers may notice their partner shifting.
- Heavier. At about 35kg for a king, it’s not easy to rotate solo. Get help.
- The price. Even on sale, it’s pricier than the Emma. Worth it if you sleep hot or prefer springs, but the price gap is real.
Who It’s For
Hot sleepers. People who prefer a bouncier feel. Those who want hybrid technology without spending Hypnos money.
Hypnos Orthos Support King Mattress
Price: ~£1,200-1,400 Type: Pocket sprung (1,400 springs in king) Trial: None (but available to try in John Lewis stores) Warranty: 10 years
Hypnos makes mattresses for the royal family. That’s their marketing hook, and it works — but more importantly, they make genuinely excellent mattresses. The Orthos Support is their orthopaedic model, designed for people who need firmer support. It’s handmade in the UK.
What We Like
- Firm support without feeling like a board. The 1,400 pocket springs create a surface that’s supportive but not punishing.
- Exceptional build quality. Hand-tufted, natural fillings (wool, cotton), proper mattress construction. You can feel the quality difference immediately.
- UK-made. Manufactured in Castle Donington, Derbyshire. Materials sourced responsibly with sustainability certifications.
- Try before you buy at John Lewis, Dreams, and Bensons — invaluable for a mattress at this price.
What Could Be Better
- No trial period. This is the biggest drawback. If you buy online and don’t like it, returning a £1,300 mattress is a headache.
- Heavy. About 40kg for the king. You’ll need two people to rotate it.
- Too firm for side sleepers. If you primarily sleep on your side, the firmness creates pressure on your shoulders. Back and front sleepers will love it.
Who It’s For
Back sleepers. People with lower back pain who need firm support. Anyone who values UK craftsmanship and natural materials over a long trial period.
Silentnight Mirapocket 1200 King
Price: ~£350-450 Type: Pocket sprung (1,200 springs in king) Trial: 60 nights Warranty: 5 years
Silentnight is the name your parents probably had on their mattress, and there’s a reason they’ve endured. The Mirapocket 1200 is their mid-range pocket sprung option, and it’s the best king size mattress you can buy for under £500.
What We Like
- The price. Under £450 for a king with 1,200 pocket springs is excellent value.
- Available everywhere. Argos, John Lewis, Dreams, Bensons — you can walk in and try it today.
- Breathable. Pure pocket sprung construction means good airflow. No foam heat issues.
- Eco Comfort fibres made from recycled plastic bottles in the comfort layers.
What Could Be Better
- Shorter trial. 60 nights is less generous than the 200-night trials from Emma or Simba.
- 5-year warranty is half what the premium brands offer.
- Less pressure relief than foam. It’s supportive but doesn’t contour to your body shape like memory foam. Side sleepers with hip pain may find it lacking.
- Edge support is basic. No reinforced edges, so the outer 15cm or so compresses more.
Who It’s For
Budget-conscious buyers who want real springs, not foam. People who want to try in a shop today. Anyone upgrading from a very old mattress who doesn’t want to spend over £500.
If you’re looking at this price range specifically, our best mattresses under £500 roundup covers all the options.
Brook + Wilde Lux King Mattress
Price: ~£750-900 (frequently discounted to £500-600) Type: Hybrid (2,000 pocket springs + memory foam) Trial: 200 nights Warranty: 10 years
Brook + Wilde is a UK brand that does something clever: you choose your firmness at checkout. The Lux comes in Soft, Medium, and Firm, using different foam densities on the same spring base. This solves the biggest problem in online mattress buying — guessing whether you’ll like the firmness.
What We Like
- You choose your firmness. No compromise. If you know you want soft, you get soft. Not a “universal” medium that’s a compromise for everyone.
- 2,000 pocket springs in a king. That’s far more than the Simba Pro or Silentnight, meaning better body contouring and less motion transfer.
- Excellent motion isolation. The dense spring count combined with foam layers makes this one of the quietest mattresses we’ve tested. Not a creak.
- 200-night trial with free exchanges. If you picked the wrong firmness, Brook + Wilde swap it for a different one instead of a full return.
What Could Be Better
- Heavier than most. 2,000 springs plus foam layers means about 38kg. Rotating it is a proper workout.
- Less well-known brand. You won’t find it in John Lewis. Online only, which means trusting the trial period.
- The “Soft” option is very soft. If you order Soft and you’re over about 90kg, you may bottom out. The Medium is the safer bet for most people.
Who It’s For
Side sleepers who want a softer mattress. Couples who want minimal motion transfer. Anyone who’s been burned by a “one firmness fits all” mattress and wants to choose.
Nectar Memory Foam King Mattress
Price: ~£450-550 (frequently discounted to £300-400) Type: Memory foam (3 layers) Trial: 365 nights Warranty: Lifetime
Nectar offers the longest trial period in the industry — a full year — and backs it with a lifetime warranty. The mattress itself is a solid mid-range memory foam option that competes directly with the Emma Original at a lower price point.
What We Like
- 365-night trial. A full year to decide. No other major brand matches this.
- Lifetime warranty. Covers manufacturing defects for as long as you own the mattress.
- Good pressure relief. The three-layer foam construction cradles pressure points well, though not quite as refined as the Emma.
- Aggressive pricing. The regular sale price of £300-400 for a king makes this the cheapest quality memory foam option available.
What Could Be Better
- Sleeps warm. Like all memory foam, it retains heat. Nectar’s “cooling” claims are marketing — it’s cooler than some foams, but warmer than any spring option.
- Slow to respond. If you move around a lot at night, the slow recovery of the foam can feel like you’re fighting it. Back sleepers who stay in one position won’t notice; restless sleepers will.
- Off-gassing. The initial chemical smell when you unbox it is stronger than the Emma or Simba. It dissipates within a week in a ventilated room, but it’s noticeable.
Who It’s For
Budget-conscious buyers who want memory foam. People who like the security of a 365-night trial and lifetime warranty. Back sleepers who don’t move much at night.
Head to Head: Which King Mattress Should You Buy?
Let’s cut through it:
- Best overall: Emma Original. The safest bet for the widest range of sleepers, with a fair price and generous trial.
- Best for hot sleepers: Simba Hybrid Pro. The spring layer and open construction keep you cooler than any foam option.
- Best for back pain: Hypnos Orthos Support. Nothing matches proper pocket sprung firmness for spinal alignment. Worth the premium if your back is the priority.
- Best on a budget: Silentnight Mirapocket 1200. Real springs, fair price, available in shops.
- Best for side sleepers: Brook + Wilde Lux (Soft or Medium). The customisable firmness and 2,000 springs create the best pressure relief for hips and shoulders.
- Best value for money: Nectar Memory Foam. The 365-night trial and lifetime warranty at under £400 on sale is hard to argue with.
King Size Mattress Buying Mistakes to Avoid
After testing dozens of mattresses, these are the mistakes that cost people money:
Buying Without Measuring
A UK king is 150 × 200 cm. Measure your bed frame and your bedroom. A king mattress in a room that’s 3 metres wide will leave you squeezing past the bed sideways.
Ignoring the Base
Your mattress is only as good as what’s underneath it. A saggy divan base will ruin even a £1,500 mattress. Sprung slats or a platform base provide the best support. If your base is more than 8 years old, budget for replacing it alongside the mattress.
Falling for Discounts
Emma is “on sale” roughly 340 days a year. Simba runs “last chance” offers every month. The “sale price” is the real price — the inflated RRP exists to make the discount look impressive. Don’t rush a purchase because of countdown timers.
Spending Too Much (or Too Little)
The sweet spot for a quality king mattress in the UK is £400-800 on sale. Below £300, you’re compromising on materials and durability. Above £1,000, you’re paying for brand prestige and natural materials — which may matter to you, but don’t automatically mean better sleep.
Skipping the Trial
If a brand offers a 200-night trial, use at least 30 nights before deciding. Your body takes 2-4 weeks to adjust. People return mattresses after one bad night, then buy something else and have the same experience. Give it time.
Where to Buy King Size Mattresses in the UK
In Store
- John Lewis — widest range of premium brands (Hypnos, Tempur, Vispring), excellent return policy, and sales staff who actually know the products
- Dreams — the biggest mattress retailer in the UK. Good mid-range selection, frequent sales
- Bensons for Beds — similar to Dreams, slightly cheaper. Worth checking both
- Argos — budget options and Silentnight range. Good for “I need a mattress today” emergencies
Online Only
- Emma — emmasleep.co.uk, free delivery, 200-night trial
- Simba — simbasleep.com, free delivery, 200-night trial
- Brook + Wilde — brookandwilde.com, free delivery, 200-night trial
- Nectar — nectarsleep.co.uk, free delivery, 365-night trial
Bottom Line
The Emma Original is the best king size mattress for most UK buyers. It’s comfortable across all sleeping positions, the price is fair (especially during sales), and the 200-night trial gives you genuine time to decide. If you’re upgrading to a king and want something reliable without spending hours researching, the Emma is where to start.
If you sleep hot, spend the extra on the Simba Hybrid Pro — the spring layer makes a real difference to temperature. If you have back problems, try the Hypnos Orthos Support in John Lewis first. And if budget is tight, the Silentnight Mirapocket 1200 is the best king mattress under £500 by a clear margin.
Whatever you choose, use the trial period properly. A good king size mattress lasts 8-10 years. That’s worth spending a month to get right.
Frequently Asked Questions
What is the best king size mattress in the UK? The Emma Original is the best overall king size mattress for most UK buyers, offering excellent pressure relief, a 200-night trial, and a fair price around £550-650. For hot sleepers, the Simba Hybrid Pro is the better choice.
How much should I spend on a king size mattress? The sweet spot for a quality king mattress in the UK is £400-800 on sale. Below £300, you compromise on materials. Above £1,000, you’re paying for premium branding and natural materials — nice but not necessary for great sleep.
Is a king size mattress worth the upgrade from a double? If your bedroom can fit one (minimum 3.6 × 3.6m room), yes. A king is 150cm wide versus 135cm for a double — that extra 15cm per side makes a noticeable difference for couples.
How long does a king size mattress last? A quality king mattress lasts 8-10 years with proper care. Rotate it 180 degrees every 3-4 months, use a mattress protector, and ensure your bed base is supportive. Budget mattresses may need replacing after 5-6 years.
Can I try a mattress-in-a-box before buying? Not in store, but most brands offer generous trials — Emma and Simba give 200 nights, Nectar offers 365 nights. If you don’t like it, they collect it for free. Use at least 30 nights before deciding, as your body needs time to adjust.