A drop-in seat deck for furniture assemblies. Various embodiments reduce the complexity and bulk of the seating frame, and also reduce the labor associated with assembly. Unlike the conventional spring suspensions, which apply constant spring loaded forces on the frame rails to maintain the springs in tension, the spring load force of the disclosed drop-in seat deck is provided by solely by the structure of the drop-in seat deck. Thus, the frame can be designed to support only the weight of the seated person is transferred to the rails of the seating frame, without consideration for pre-loading the seat deck. In various embodiments, dimensional changes to the seat deck occur under load. In some embodiments, these changes are accommodated by enabling a free end of the seat deck to slide on a support surface; in other embodiments, the changes are accommodated by flexures that are integral to the seat deck.