The cushion includes a seat and a back separated from each other by a seat-sacral hinge to define two separate air fillable spaces. Separate fill port tubes are provided for filling and adjusting level of fill within the seat and back of the cushion. Weld lines are provided within the seat to define separate chambers within the seat but which are joined together by a common manifold. Weld lines within the back of the cushion divide the back into a sacral/hip space and a sacral/lumbar/kidney space, as well as various back chambers above the sacral/lumbar/kidney space. The cushion includes webs that support dowel pockets that receive dowels for removable attachment of the cushion to an underlying chair. As an alternative, the cushion can be built into the chair.