A seating device and seating device backrest are described. The seating device and backrest have a seat portion dimensioned for an occupant; a support arm coupled to seat portion proximate a first end of the support arm; a mounting receptacle coupled to the support arm proximate a second end of the support arm, wherein the mounting receptacle is configured to accept a substantially convex body, and wherein the support arm is configured to position the mounting receptacle at an angle such that the convex body makes focal contact at an seat occupant's optimally concave lumbar/thoracic spinal regions.