A chair including a seat member for supporting a user, a backrest member mounted on the seat member, an adjustable platform attached to the backrest member in which the adjustable platform is selectively adjustable to provide a desired contour for supporting the back of a user seated within the chair, and a multipoint adjustment mechanism configured to adjust the adjustable platform along multiple locations of the platform to provide a desired contour for supporting the back of a user seated within the chair. The chair may be custom fitted to a specific user where the curvature of a user's back (e.g., in the spinal region) is measured relative to an idealized curvature, and the multi-point adjustment mechanism of the chair may be dialed in to improve the user's posture as the user uses the chair.