This mattress is truly an extra firm when it comes to the springs. Even laying on top as a big person you won't feel any lack of spring support. The isolation between sides is great as one person can be turning and the other would hardly be able to tell. The top layer is the opposite story. It is very soft, but not in a comfortable way. You sink into it in such a way that it gives all sorts of strange pressure causing pain. I think its either the gel foam lumber support or duracool they advertise as a feature causing it, but the experience is neither cooling or supportive.  If they got rid of the top layers it would be the perfect base mattress that you could add whatever topper you wanted to, but unfortunately the top layer ruins it.