I recently had shoulder surgery and purchased the 4 inch mattress topper for a sofa-bed that I’ve been sleeping on.  The original mattress is very thin.  I like the fact that the topper has a cover.  The topper has added comfort, thickness and softness to my sleeping on my back. Unfortunately, since I sleep on one side, the place where I sleep shows an indentation on the topper. So I have to move the topper every time I change sheets.