Should a bed be firm if I have back pain?
That is a stubborn misconception. Too firm actually pushes the spine crooked for side sleepers. What matters is whether your back lies straight in the position you spend most hours in.
The right bed and pillow keep your spine in a neutral line, and what that takes differs per sleeping position. Side sleepers need pressure relief at shoulder and hip, plus a higher pillow; back sleepers more support in the lower back and a lower pillow; front sleepers a firm base and a very thin pillow or none at all.
As a side sleeper your shoulder and hip bear most heavily on the bed. Those points must be able to sink while your waist stays supported — otherwise your spine sags or is pushed upwards instead.
The pillow fills the space between shoulder and neck and is therefore higher and firmer than for other positions. The broader your shoulders, the higher that pillow may be.
On your back you want the lower back supported without the hips sinking. The pillow is lower, so the neck doesn't crane forward.
Sleeping on your front puts the most strain on lower back and neck. A firmer base stops your waist from sagging, and a very thin pillow or none at all keeps the neck neutral. Anyone who sleeps on their front and has complaints usually gains more from a different position than from a different bed.
In a showroom you lie down consciously, usually on your back, in your clothes, during the day. That is not how you sleep. The position you spend most hours in is chosen by your body unconsciously, in the dark.
What you judge the next morning is therefore not whether you lay comfortably, but whether you get up without stiffness and how often you changed position during the night.
That is a stubborn misconception. Too firm actually pushes the spine crooked for side sleepers. What matters is whether your back lies straight in the position you spend most hours in.
Yes, and that is exactly what a build-up per half exists for. With a large difference in weight or position, that choice weighs more heavily than which model you take.