You really, really need to spend a decent amountof time lying on the mattress before you choose one.
We were going to go for a pocket sprung 2k springs mattress (about £500-£800 for a double from memory) but then tried out the memory foam matresses.
As a couple we preferred the memory foam, I particularly like the way that you partner can roll around and you barely notice it whereas for some reason (even on 2000 springs) you tend to notice it on sprung mattresses.
I am not sure that a memory foam mattress can "breathe" as well as a pocket sprung, I think it unlikely. However so far I am very happy with our mattress choice.
As for beds - I hate divans with a passion. I hate cheap bedframes with hardboard over the frame. I prefer sprung beds or beds with wooden slats (generally curved up) that give a little extra "spring" to the bed.
There's been a glut of bed threads recently..... is it because of excessive bed advertising?