Abstract: A mattress includes a plurality of individual foam blocks which are secured together using one or more plastic fasteners to form a five-sided foam encasement. A spring unit is fittingly disposed within an interior cavity defined by the foam encasement. One or more top layers of foam rubber are mounted on the foam encasement over the spring unit and are secured thereto using additional plastic fasteners. An outer layer of quilted cotton material is sewn over the foam encasement and top layers of foam rubber to yield the finished one-piece mattress. As can be appreciated, the outer periphery of the mattress is defined by foam material, which is substantially rigid in its construction, rather than the spring unit, which is highly susceptible to warping. In this manner, the foam material serves to preserve the shape of the outer periphery of the mattress over time.