Abstract: The disclosed seat cushion has a padded member, defining a wedged shape that is pointed rearwardly; and a flexible fabric case encloses such padded member. Ties on the case are used to removably secure the seat cushion to the chair, so that the rear wedged shape of the cushion is located just forwardly of where the seat of the person, sitting on the chair seat, actually makes contact with the chair seat; and the person's legs cross over the seat cushion. The wedge angle may be between 20 and 40 degrees. The case fabric has a high degree of roughness and friction against the clothing of the person that will sit on the chair and over the cushion, such as of a duck or canvas material. The padded member is of a firm foam, to resist being deformed by the weight of the person who will normally be sitting on the cushion, to a dimension less than approximately between 10% and 40% that of the original dimension.