A body-conforming booster cushion seat having a malleable filler material so as to permit the cushion to conform to the body shape of a user when the user is seated thereon. The booster cushion seat includes a strap for securing the cushion to the chair, and the height of the cushion may be adjusted by adjusting the tension on the strap. The bottom of the cushion is provided with a textured base to prevent slipping when the textured base contacts a corresponding surface, and a safety belt is included to secure a juvenile user in place on the booster cushion seat.