A mattress having a wedge-shaped mattress body with an inclined upper surface, the upper surface divided by a transverse breast concavity into a head-supporting portion and a body-supporting portion. The mattress has a flat position in which the concavity is open to receive breasts as well as an upright position in which the concavity functions as a hinging mechanism and the mattress is held in the upright position by adjustable mechanisms. In the flat position the mattress may be used in the prone position, laying on the back, or in a yoga position. In the upright position, the mattress may be used laying on the back and partially sitting upright, or, by adjusting the position of the mattress, sitting upright.