Your bed needs to be breathable. That's the single most important thing. A cool bed without proper ventilation will attract condensation and mold, and make you feel damp. A good spring mattress sitting on top of slats will never get uncomfortably hot or cold in any particular spot, because air moves freely in and out, powered by your own body movements. The mattress should also be as firm as you can tolerate. A firm…
If you want an all-natural, chemical-free, traditional hand-made pocket-sprung mattress you’re looking at £3-6k here in the UK. But I agree they are the pinnacle of mattresses, ticking every box