I've recently bought an Emma Mattress. It's made from various layers and grades of foam, and I absolutely love it, I've never been so comfortable. It stays very smooth and even, not bouncy, so even if I had a partner in the bed, I think we'd both sleep well without disturbing each other. (This is a matter of conjecture, as I am widowed and may never get the chance to try it out with a partner!)
I chose this because Which? recommended it so highly. I ordered online, so didn't get the chance to try it out, but I have no regrets. Not cheap, but they always seem to have some sort of offer on. They say they'll take it back after 100 days if you don't like it. Well, they're not getting this one back!