Mattress Online Rock Hard Ultra Firm Mattress
Mattress
Mattress Online Rock Hard Ultra Firm Mattress
Size
Firmness
Firm
Construction
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.
- 75cm each, every night: Two sharing get 75cm of width apiece, which means you can change position without negotiating for territory.
- Extra length for taller sleepers: At 200cm the UK king is 10cm longer than the UK double, a real relief if one of you is nudging six foot on a surface with almost no sink.
- Different schedules, less disturbance: An all-foam build with very little bounce, spread across a king width, means an early riser can slip out with less chance of waking their partner.
- Firm support you can push against: The extra-firm surface holds you on top of the bed, which makes getting in and out easier if you're recovering from injury or surgery.
- Fits most master bedrooms: We suggest allowing at least 2.7m x 2.9m, which most UK master bedrooms manage even once wardrobes go in.
- Compare live king prices: The prices shown on this page are updated as retailers change them, so you're always seeing the current cost for this size.
This size suits you if...
You share the bed every night and a UK double has started to feel like a squeeze, or one of you keeps different hours and wants room to get up without waking the other. It also makes sense if either sleeper is tall, since the 200cm length gives welcome extra room on a surface this firm, where you lie on the mattress rather than sinking into it.
Consider another size if...
Your room 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 and still suits a solo sleeper comfortably.
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Is the Rock Hard Ultra Firm in a UK king big enough for two?
Yes. At 150 x 200cm, two people sharing get 75cm of width each. On a mattress this firm that space goes further than it would on a soft one, because you stay where you lie rather than drifting towards a dip in the middle. Couples who move around a lot in the night will feel the benefit most.
How much bigger is the UK king than the UK double in this mattress?
The UK king is 15cm wider and 10cm longer than the UK double, which gives each of two sharers 7.5cm more width. That sounds modest on paper, but it's roughly an extra hand's width of personal space per person, and the added length helps anyone approaching six foot.
What room size do I need for this mattress in a UK king?
We suggest allowing at least 2.7m x 2.9m, with more if you can manage it. New build master bedrooms often look generous empty but tighten up quickly once wardrobes and drawers are in, so measure with your furniture in mind, and leave walking space on both sides of the bed.
Should I get the UK king or the UK super king?
The UK king is 30cm narrower than the UK super king; both are 200cm long. The UK super king gives 90cm each for two sharing against the UK king's 75cm, but we suggest at least 3m x 2.9m of room for it. If your bedroom is average sized, the UK king is the safer fit.
Will a king size firm mattress help if my partner gets up earlier than me?
It should. The all-foam build has very little bounce, so movement on one side carries less to the other, and the UK king's 75cm per person means an early riser can swing out from their own edge rather than clambering past you. It won't make a heavy-footed partner silent, but it reduces the ripple.