As you might have already figured out, sitting on the edge of a new-ish mattress isn't the same as sleeping in one. It sounds like what you want is a bed that springs back more readily. Traditional coil mattresses tend to retain body shape longer than a memory foam mattress, but a memory foam mattress reacts to body heat (which is how it works). If you don't like the feeling of sinking into a giant pillow (which is what pillow tops tend to do), then might I suggest either a memory foam mattress or a hybrid, which has memory foam on top and coils underneath?