A bed mattress including an outer casing adapted to house one or a plurality of different supportive materials within said casing (1) in distinct transverse regions wherein fixed supportive materials (7, 9, 11) are provided at the top and bottom regions of said mattress corresponding to the head and foot regions of a user; and an intermediate region so formed between is provided with a transverse assay of fixed supportive materials (11) having vacant regions between adjacent materials, wherein said outer casing has a plurality of ports (4) corresponding to said vacant regions which are adapted to facilitate the ready insertion, removal and/or replacement of one or more auxiliary supportive materials (10) so as to allow the user to vary the supportive quality of said intermediate region of said mattress.