Mattress Online Rock Hard Ultra Firm Super King Mattress
The Rock Hard Ultra Firm from Mattress Online is an all-foam orthopaedic mattress rated extra firm, which means very little sink and a sleeping surface that keeps you on top of the bed rather than in it.
- Very firm, no sinking feel
- Moulds to ease pressure points
- 100-night trial
£529
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Mattress Online Rock Hard Ultra Firm Mattress
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Mattress details
Mattress
Mattress Online Rock Hard Ultra Firm Mattress
Size
Firmness
Firm
Construction
Foam
Orthopaedic
Depth (cm)
25
Layers
3
Layer Details
Reflex Foam
A flexible reflex foam layer sits at the top, which means responsive support that helps keep your spine aligned. It has a little give, but this is not a plush comfort layer.
Ortho PU Foam
The ortho PU foam core provides the extra-firm support this mattress is built around. It moulds to your shape to reduce pressure points and encourage better posture.
Reflex Foam
A second reflex foam layer at the base promotes spinal alignment from underneath. It moulds slightly to your body for a more personalised feel.
Layer details from mattressonline.co.uk product page, September 2026.
Key benefits
- 90cm of width each: Two people sharing get 90cm each, which means your own clearly defined stretch of bed rather than a nightly negotiation over the middle.
- Distance beats a fidgeter: With a genuinely restless partner, the extra width does more than any comfort layer could: they can turn all night without reaching your side.
- Firm surface, less roll-together: The extra firm reflex and ortho PU foam keeps the surface flat across the full 180cm, so neither sleeper drifts into a dip in the centre.
- Room for the whole household: When children wander in at 3am or a large dog treats the bed as home, a super king means everyone keeps a workable share.
- Wider than a UK king, same length: The UK super king is 30cm wider than the UK king and the same length, so you gain width without needing a longer wall.
- Know your room first: We suggest allowing at least 3m x 2.9m so you can still open drawers and walk round the bed comfortably.
This size suits you if...
You share the bed every night and want the maximum separation a standard UK size offers, your partner is restless and you have given up on comfort layers solving it, or children and pets regularly join you and a UK king no longer stretches far enough. You should also have the space: a room of at least 3m x 2.9m, and a genuine preference for a very firm bed.
Consider another size if...
Your bedroom falls short of the 3m x 2.9m we suggest, or a bed this wide would crowd the room. We'd recommend the UK super king's nearest sibling, the UK king, instead: it's 30cm narrower, the same length, and needs at least 2.7m x 2.9m.
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FAQ's
How much space do two people get on the Rock Hard Ultra Firm super king?
You get 90cm each for two people sharing, which is the most personal space any standard UK size offers. On a mattress this firm, that width matters: there's no soft centre to drift towards, so each sleeper stays on their own flat, supportive patch all night.
Is the UK super king a good choice for restless couples?
It's arguably the best reason to buy one. All-foam builds like this transfer less movement than open coil designs to begin with, and 90cm each adds physical distance on top. A partner who turns constantly, or gets up at odd hours, becomes far easier to sleep through.
Should I get this mattress in a UK king or UK super king?
The UK super king is 30cm wider than the UK king and the same length, and the UK king gives 75cm each for two sharing, so the UK super king gives 15cm more each. If your room meets our suggested 3m x 2.9m, take the extra width; if not, we suggest at least 2.7m x 2.9m for the UK king.
Will the Rock Hard Ultra Firm super king work for sharing with children or pets?
Yes, and it's a sensible pick for it. The extra firm surface stays level under uneven weight, so a child sprawled sideways or a large dog at the foot doesn't tilt anyone else's side. With 90cm per adult, an unexpected visitor still leaves everyone a usable share.
Can I get a super king Rock Hard Ultra Firm upstairs easily?
At 180 x 200cm it's the trickiest standard size to move, so measure landing turns, door swings and the stairwell before ordering. Mattress Online doesn't publish a weight for this mattress, and as an all-foam design it will flex a little but shouldn't be folded, so plan for two people carrying it.