We've got a Sealy Posturepedic and love it. I think there are 3-4 different models/levels of firmness and we went with the 2nd most firm. When testing the firmest was slightly uncomfortably when sleeping on the side (which the GF does a lot).
Sealy basically makes the best mattresses on the floor. When I told the sales guy, after trying several other brands/models, they seemed to feel the best (and were rated as such) he basically said "there's a reason Sealy's don't run a lot of sales"; they don't need to. When they do it's all factory based, so unless a store is going out of business, they are usually the same price everywhere.
Hope this helps someone.