A body support structure includes a body support member and a base having an upper component coupled to the body support member and a lower component adapted to be supported on a floor. An adjustable spring mechanism biases the body support member. A weighing mechanism is coupled to the adjustable spring mechanism. The weighing mechanism includes a height adjustment device disposed between the upper and lower components of the base. The height adjustment device includes a pneumatic spring having a pressure tube coupled to the lower component and a piston rod extending upwardly from and moveable relative to the pressure tube. A housing is disposed around the pneumatic spring and is coupled to the upper component. An adapter is coupled to the piston rod. A weighing spring is disposed between the adapter and the housing, with the housing moveable relative to the adapter between first and second weighing positions.