Some kneeling chairs come without a backrest but will still aid posture by making the sitter rest upright to stop sliding off the angled seat and knee pads. They take a little getting used to ...

Fdit Ergonomic Kneeling Chair Adjustable Posture Correction Knee Stool with Back Support for Home and Office Angled Posture Seat Posture Chair Black on sale, Home Office Posture Corrector for Chair ...