One of my projects, when I finish all the others, is to write a book on memorisation, and techniques for memorising things, such as poems, Scripture, play scripts, speeches. I haven't yet seen a book that really gets to grips with most of these, though it may be out there hiding from me.
I was reminded of this (memory technique!) by seeing the phrase memory foam topper. I had to go and check it out. Turns out it merely means material that, when you put your hand behind it, retains the shape of your hand. Or, more correctly, when you're trying to get to sleep, it takes on the contours of your body. It sort of sounds useful, though I'm not entirely convinced. In the same advertising there's something called convoluted toppers, which turn out to look like a large extended egg carton that you sleep on. You can use the peaks up or down, depending on your preference. I don't see me sleeping on this stuff personally, although no doubt there are people who swear by it. I'd probably have nightmares about being an egg whose shell was breaking.
We've got a good solid mattress on our bed that we've now had for a number of years; it has give in it, but not enough to give way, so you're always feeling firmly supported. The bed at our daughter's house in Christchurch (where we were babysitting for the last few days) is similar: you have none of that awful sinking feeling when you get into it. The mattress we had for a number of years (before the current one) used to throw us together in the middle of the bed. This has its points but isn't ideal long-term.
I'm not sure that mattresses that take on the shape of your body are actually better for you than ones that give you firm support. Each to his/her own, I guess.