I remember reading in an article that states that sleeping on hard surface is actually no good for your health, the reason being our body contour is not as flat as a board, so when you lie down on a flat hard surface, not all of your entire back body is supported. The best way is to get a mattress that's firm enough to support you, but soft enough to make a contour around your body curve. Ideally a memory foam would achieve something like this, that's why they become so popular nowadays.
Happy sleeping!