Abstract: Described in the prior art, but uniquely more modifiable for the present invention, is the general concept of horizontally framing horizontal sleeping mattresses with resiliently compressive elongate resinous bars, especially bars constructed throughout of polyurethane resinous materials. Departing from the prior art, the present invention describes, for selectable horizontal mattresses, a surrounding framework wherein the four confronting elongate resinous bars are self-interlocking in cornerwise relationship with the abuttably surrounded horizontal mattress. Such self-interlocking relationship for confronting bars is enabled by unitarily constructing within inter-bars confrontational portions, specially constructed and locatable tongue-and-groove mateable capabilities, and thusly satisfying the sought objectives of the present invention.