Not too Hard and Not too Soft

When I am pregnant, I easily get backache. If I lie down on the floor, I will have hard time getting up without feeling the pulling on my back bone. If I sleep on a soft bed, I will wake up with a backache. So my bed must be just nice. Not to hard and not too soft. Looks like I need to spend to buy me a new bed??? I wonder whether the sleep number bed will work wonders.