We recently got one of those foam mattresses over the traditional coil one.
It's okay... it was expensive and I don't really like it but that's maybe because I'm really heavy so it's not as supportive as I would have hoped. It's firm when you lie on it but the edges and corners sink easily so it's not a bed that you can sit on the edges.
I wanted to get one of those online ones because of the money back guarantee but the boss wanted to try it in person and get it from a place that would take our old mattress. I don't recall the brand offhand, it was one of those S ones, Sealy or Serta and we got it at Living Spaces (cost over $1k... gah). She also wanted it because you can wash the cover and she thinks it's bug resistant.
Hopefully in a few years we can go back to a coil mattress.