a stiffening system for the perimeter edges of a foam core mattress comprising a coil spring structure disposed along one or more perimeter edges of a mattress having a foam sleeping area . the perimeter spring structure is rectangular or square in cross - section and provides sufficient stiffness for comfortable seating on the edges of the mattress and is joined to the foam core by planar fabric elements that span the joint between them and are attached to both . the sleep area provides the softness and other salutary effects of a foam sleeping surface while the stiffer spring perimeter element provides the rigidity need for comfortable seating and wear resistance .