Is there any sort of general buying guide or handy tips for at least narrowing down mattress options? Like minimum spring count, types/technologies to generally avoid, how to genuinely tell if one will last, that type of thing? It's such a frustrating thing to try to buy. I have literally no idea what I'm looking for. I mean I settle on a firmness and size obviously, but then I go to several stores and try a bunch out, and they all feel too similar to make any sort of informed decision, with sometimes hundreds of £s in it between the options. It just feels like an absolute gamble whether or not you end up with one you end up liking..