A bed is provided that includes a foundation configured to be positioned on an underlying floor and a mattress assembly supported on and secured to the foundation. The mattress assembly includes a base layer and a body supporting portion. One or more internal plates are interposed between the base layer and the body supporting portion of the mattress assembly and are maintained at a fixed height relative to the underlying floor. The foundation and the mattress assembly are moveable between at least a first predetermined height and a second predetermined height relative to the underlying floor. As a result of the movement of the foundation and the mattress assembly between the first predetermined. height and the second predetermined height, the one or more internal plates apply pressure to and compress the body supporting portion of the mattress assembly, thus increasing the firmness of the body supporting portion.
