Abstract: A unitary base member for supporting a wire spring assembly of a bed foundation. The base member includes a lattice formed of a plurality of lateral members and a plurality of longitudinal members. The lattice has a lower surface and an upper surface for mounting a wire spring assembly thereon. The lateral members are oriented substantially parallel to each other, and the longitudinal members are oriented substantially parallel to each other. The plurality of lateral members are positioned above said plurality of longitudinal members. Significantly, the lateral and longitudinal members of the lattice are integrally and inseparably formed together with each other as a single piece of substantially rigid plastic for preventing movement of the members with respect to each other.