Futon, for sleeping on. Used to wake up in the middle of the night with agonising cramp in my back, it reduced it by maybe 95%. Granted a new good bed might have achieved the same but I don't think I'd ever go back to a bed at this point.
I found the same effect just by giving up spring beds. I now sleep on latex, but did the foam thing for a while (T&N used to have an 8" bed I loved).
Honestly, mostly I was just so fed up with my bed at the time I actually started sleeping on the floor with a duvet for padding. I chose that one because it would arrive the quickest at the time.
I got the idea from travelling, in Japan and staying with a friend in Thailand who just had this rubber/latex pad on the floor. Slept really well so I decided to give it a try at home.