King-Size Mattresses

King-size mattresses: what to look for

A king-size mattress measures 150 by 200cm in the UK standard, sized for two adults who want enough space not to disturb each other. The size jumps from a double (135cm wide, only 67.5cm per person) are 15cm of extra width - meaningful in real terms. Most British couples should be looking at king-size as the default, not as the upgrade.

The brand spread is roughly the same as the wider mattress market. Silentnight, Sealy and Sweet Dreams cover the £300 to £700 mid-market with pocket-sprung and hybrid memory-foam constructions. Sleepeezee and Slumberland sit at £600 to £1,500 with higher pocket-spring counts and natural-fibre fillings. Hypnos occupies the £1,500-£4,000 premium tier with hand-tufted construction and Royal Warrant heritage.

Construction matters more at king-size than at smaller sizes, because the surface area is bigger and any sag develops in patterns rather than a single dip. Pocket-sprung counts of 1,000+ are the comfortable spec; below 1,000 and the springs are spaced widely enough that motion-transfer between sleepers becomes noticeable. Reinforced edges (often called "side-stitched") stop the mattress collapsing where you sit to put socks on.

Delivery is the practical thing to plan for. King-size mattresses don't fit through some narrow stair turns, particularly in older British houses. Roll-packed mattresses (the bed-in-a-box format) sidestep this problem; traditional flat-packed mattresses might not. Measure the route before ordering.

Choosing firmness for two people of different weights

A king-size sleeps two adults, and unless those two adults weigh roughly the same, the firmness decision needs more thought than a single-sleeper buy. UK retailers rate firmness on a 1-to-10 scale, where 1 is the softest and 10 is orthopaedic-board level. Couples within 15kg of each other usually agree on medium or medium-firm (5 to 7). Outside that, the heavier sleeper sinks more on a soft mattress, hitting the firmer base layer; the lighter sleeper stays on the comfort layer and feels under-supported on a firm one.

The standard fix is a hybrid pocket-sprung mattress with a layered comfort top. Pocket springs respond locally rather than transmitting movement across the bed, so partner weight asymmetry matters less. Sealy and Sleepeezee build dual-firmness king-size models (one half medium, one half firm) for couples with a large weight gap. They cost £100 to £300 more than single-firmness equivalents and are sold mainly through specialists like MattressNextDay rather than the high street.

Memory foam alone is the wrong answer for couples with a weight gap. It sinks where it's pressed and slowly recovers, so the heavier sleeper rolls slightly toward the heavier-loaded half. Couples who like the foam feel should go hybrid (foam comfort layer over pocket springs) for the asymmetry-handling, not all-foam.

King-size or super king? The 30cm decision

A king is 150cm wide; a super king is 180cm. That extra 30cm of width is the only real difference (length is the same, 200cm for both standard). Per sleeper, a king gives 75cm of width; a super king gives 90cm. For context, 75cm is around the width of a single mattress, which is the right way to think about whether king is enough.

Super king makes sense in three situations. The bedroom is over 4m wide (super king plus bedside tables needs 280cm to 300cm minimum, depending on side furniture). One or both sleepers exceed 6ft tall and want shoulder room to side-sleep without overlap. Or there are children or pets joining the bed regularly. Outside those three, the king at 30cm narrower usually fits the room and the budget better, and bedding is easier to find.

The bedding point is real. Super king fitted sheets are 30% more expensive than king on average, and ranges are narrower at most UK retailers. Dunelm and John Lewis stock super king across most ranges; smaller retailers stock super king for premium ranges only. Budget around £20 to £40 extra per bedding set if you go super king.

The brands and retailers we list

We pull around 9,900 king-size mattresses from across the UK retailer network.

MattressNextDay is the deepest king-size catalogue, with named-day delivery on most lines.

Mattress Online and Mattress Man cover the upper-mid bracket with a strong brand spread.

Robert Dyas stocks the value-to-mid bracket including roll-packed and bed-in-a-box options.

Read our mattress buying guide for the firmness, position and weight decisions. Filter the grid above by brand, depth or price to narrow things down. Prices update daily.

Trial periods and what they actually cover

Most UK mattress retailers now offer a sleep trial, where you can return the mattress for a refund if it does not suit. The standard is 100 nights at MattressNextDay, Mattress Online, and most bed-in-a-box brands (Emma, Simba, Eve). Some go further. Hypnos and Hypnos-aligned premium specialists offer 60-day comfort exchanges rather than full returns. The Range and Argos run 14 to 30-day standard returns rather than trial periods, since they sell across categories rather than mattress-first.

Trial conditions matter as much as duration. Most trials require the mattress to be in the home for a minimum period (usually 30 nights) before a return is considered, since memory foam and hybrid mattresses need a few weeks for body-adjustment. Almost all trials require the original packaging or a collection visit; few accept returns of mattresses that have been visibly stained.

Read the trial terms before ordering, especially for bed-in-a-box mattresses. The unboxing destroys the original compression packaging, so collection is the only return route, and the retailer (not the courier) decides what counts as fit for collection.