Jay-Be Flex Ultra Firm E-Pocket 1200 King Size Mattress in a Box
The Jay-Be Flex Ultra Firm E-Pocket 1200 is a boxed mattress built for people who want genuinely firm support, not the medium-firm feel most brands settle on.
- Ultra-firm for back & front sleepers
- Foam-free with recycled fibres
- 10-year guarantee
£449.23
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Jay-Be Flex Ultra Firm E-Pocket 1200 Mattress in a Box
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Mattress details
Mattress
Jay-Be Flex Ultra Firm E-Pocket 1200 Mattress in a Box
Size
Firmness
Extra Firm
Construction
Foam
Pocket Spring
Rolled
Eco-Friendly
Depth (cm)
21
Layers
3
Layer Details
Advance e-Fibre™
A deep-quilted top layer of Advanced e-Fibre, which gives the sleep surface a softer first impression than the name ultra-firm might suggest. It also wicks moisture, which means better temperature regulation through the night.
Firm e-Fibre™
A densely packed comfort layer that delivers a firm feel with some pressure relief. This is where the mattress earns its firmness rating, sitting between you and the springs.
Ultra-Firm Sprung Core
The support layer, engineered for stability that lasts. It keeps the mattress from softening into a dip over time, which means consistent support night after night.
Layer details from jaybe.com product page, September 2026.
Key benefits
- Proper space for two firm-mattress sleepers: With 75cm each for two people sharing, you can lie flat on your back, the position this ultra-firm feel is built for, without negotiating elbow room.
- Less disturbance on different schedules: A firm, stable surface plus the UK king's extra width means an early riser can slip out with less movement reaching the other side.
- Extra length for taller sleepers: The UK king is 10cm longer than the UK Double, so anyone approaching six foot stops sleeping diagonally or dangling their feet.
- A firm edge to push off: That ultra-firm sprung core gives you something solid to press against when getting in and out, useful if you're recovering from injury or in late pregnancy.
- Slim depth suits standard king frames: At 21cm this sits neatly on a king divan or bed frame without towering over a low headboard, and king fitted sheets stay put easily.
This size suits you if...
You share the bed every night and a double has started to feel like a compromise, especially if one of you keeps to the edge to avoid disturbing the other. It also fits if either partner is tall and needs the 200cm length, or if you both want genuinely firm support and enough width to lie flat on your backs without touching.
Consider another size if...
Your bedroom falls short of the 2.7m x 2.9m we suggest for a UK king. In that case the UK double would suit you better: allow at least 2.6m x 2.8m for that size.
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FAQ's
Is the Jay-Be Flex Ultra Firm in a UK king good for couples?
Yes, and arguably it's the size that makes most sense for two. Firm mattresses reward lying flat, and the UK king's 75cm each for two people sharing gives you both room to do that. Across a narrower size, one partner often ends up perched near the edge; the king removes that problem.
Is a UK king long enough if my partner is over six foot?
For most people, yes. The UK king measures 150 x 200cm, and that 200cm length, 10cm more than the UK Double, is usually the difference between feet on the mattress and feet hanging off it. If your partner is well over six foot, factor in headboard and pillow space too.
What room size do I need for this mattress in a UK king?
We suggest at least 2.7m x 2.9m so you can walk round both sides and open drawers comfortably. New build master bedrooms can be tighter than they first appear once fitted wardrobes go in, so measure the usable floor rather than the room on the plan.
Will the UK king reduce disturbance if we wake at different times?
It helps on two fronts. The extra width means the person getting up at 5am isn't clambering past their partner, and the ultra-firm sprung core keeps the surface stable rather than bouncy, so movement transfers less. If one of you leaves hours before the other, the upgrade from a double is noticeable.
Where can I check the price of the Jay-Be Flex Ultra Firm in a UK king?
Use the comparison table on this page. The prices shown here are updated as retailers change them, so it's a more reliable guide than a figure quoted in a review that may be weeks old. Check the retailer's own page before ordering to confirm the size selected is the UK king.