Yeah, also, you can get something for example 8k, that will give you same support as a 15k bed, but won't last as long(something like body weights etc plays role), eg a 80kg person it may last 20 years and maintain support for that lifetime, but 120kg on it, it starts failing after 5years. It comes down to personal usage, and don't forget comfort, ie, firm does not mean better, (eg. I can't sleep on firm beds, cuts circulation on my skinny backside), you need support and comfort, again, support != firm, however, firm can be softer due to body weight, ie my 'firm', is someone else 'plush' cos I weigh nothing and end up sleeping 'on top' of it, not 'on' it (if that makes sense). A good way to check if you're getting enough support when testing in stores is, put your hands(back of hand on back) in the hollow of lower back when lying flat on your back and slide them out sideways, you want a little 'middle ground' resistance, if you just pull em out easily you're 'on top', not sinking in enough to reach support layers, if heavy resistance(like squashing em), its too soft, you're sinking into it too much, no resistance in mattress so no support at all... you need to be goldilocks, and get whats right for you personally