Hypnos Cawthorne Extra Firm King Size Mattress
The Hypnos Cawthorne Extra Firm Mattress has 1000 ReActive pocket springs under a wool and polyester comfort layer, which means you get very firm, level support with a little cushioning on top.
- Extra-firm feel for back sleepers
- Edges reinforced with firmer springs
- Wicks away moisture as you sleep
£845
Get the lowest price we've found
Save with the previous model
Some retailers still sell the earlier version of this mattress for less than the current model's best price.
Hypnos Cawthorne Extra Firm Mattress
More available sizes
Mattress details
Mattress
Hypnos Cawthorne Extra Firm Mattress
Size
Firmness
Extra Firm
Construction
Pocket Spring
Wool
Depth (cm)
26
Layers
4
Layer Details
Pocket spring core
A core of 1000 ReActive springs, each enclosed in its own fabric pocket. Each spring works independently, so the support follows your body rather than moving as one block.
Dual density eOlus fibre pad
A dual density fibre pad that supports the spring unit and helps spread pressure evenly. That means your weight is shared out across the surface rather than concentrated in one spot.
Wool and polyester comfort layer
A blend of wool and polyester fibres that adds comfort and enhances the firm feel. You get a little cushioning without losing the extra firm character.
Cotton and polyester layer
An absorbent blend of cotton and polyester that wicks moisture away from your body. It helps the surface feel drier through the night.
Layer details from mattressonline.co.uk product page, November 2026.
Key benefits
- More room each than a UK double: You get 7.5cm more each than on a UK double, which means fewer elbows and more space to settle on your back without brushing your partner.
- Length for taller sleepers: At 200cm long, the UK king is 10cm longer than the UK double, so a partner over six foot is less likely to have their feet hanging off the end.
- Less disturbance on early starts: The 1000 springs each sit in their own pocket, which means one partner getting up hours before the other should cause less movement across a UK king.
- Firm edges on a wider bed: Firmer outer springs reinforce the edge, so you can sleep near your own side of a UK king without feeling you might roll off.
- Easier getting in and out: A reinforced edge and a very firm surface give you something solid to push against, which helps if you're recovering from an injury and climbing out slowly.
- Standard bedding fits: The UK king measures 150 x 200cm, or 5ft x 6ft 6in, and takes king sheets and a 230 x 220cm king duvet.
This size suits you if...
You share the bed every night, you both prefer a very firm surface, and a UK double has started to feel tight, especially if one of you is over six foot or you're up at different times.
Consider another size if...
Your bedroom is under our suggested 2.7m x 2.9m, or you sleep alone. We'd recommend the UK double instead, which needs at least 2.6m x 2.8m.
Similar Mattresses in This Price Range
Did you know? On Mattress Unboxed we have over 1,000 different mattresses to suit all types of sleepers. View all mattresses.
FAQ's
What size room do I need for a Hypnos Cawthorne Extra Firm UK king?
We suggest at least 2.7m x 2.9m for a UK king, and 3.2m x 3.2m is more comfortable. New build master bedrooms can feel smaller once wardrobes go in, so measure with the doors open and allow space for bedside tables on both sides before you buy.
Is a UK king Hypnos Cawthorne Extra Firm big enough for two people?
For most couples, yes. A UK king gives 75cm each for two people sharing, 7.5cm more each than a UK double. If one of you sprawls or the dog sleeps on the bed every night, the UK super king gives 90cm each, though it needs at least 3m x 2.9m.
Is the Hypnos Cawthorne Extra Firm king size long enough for someone over 6ft?
The UK king is 200cm long, 10cm longer than the UK double. For a partner over six foot, that extra length is often the real reason to size up. The UK super king is the same length, so going larger only adds width, not length.
Will I feel my partner move on the Cawthorne Extra Firm in a king size?
Each of the 1000 springs sits in its own fabric pocket and works independently, so movement on one side should travel less. Combined with 75cm each on a UK king, it suits couples on different schedules, although a very firm bed won't absorb movement in the way soft foam can.
Should I get the Hypnos Cawthorne Extra Firm in a UK king or a UK double?
Choose the UK king if you share and want more room: it's 15cm wider and 10cm longer than the UK double. The UK double needs at least 2.6m x 2.8m, against 2.7m x 2.9m for the UK king, so measure first, then compare the retailers listed on this page.