A composite mattress includes a base panel of a cover, a base layer, a pressurizable layer, an intermediate layer, a top layer, and a top panel of the cover. A foundation, or rail, laterally surrounds the pressurizable layer, the intermediate layer, and the top layer. A periphery of the cover laterally surrounds the foundation and, with the top panel and the base panel, encases the other components of the composite mattress. A coiled spring layer may also be included in the composite mattress. The composite mattress may include a separable top and bottom; these elements may be modular, enabling individuals or couples customize a mattress by selecting one or more tops from a plurality of available for use with one or more bases from a plurality of available bases.