Abstract: The entire assembly includes an upper supporting panel, a base, and spring body means between the panel and base. The panel comprises a rectangular border frame and a grid made up of a series of grid wires extending longitudinally and another series extending laterally to define rows of rectangular openings serving as spring seats. The spring body means comprise coil spring bodies and attachment heads made up of single lengths of wire. The heads are bent to U-shape with a rectangular pattern similar in size and shape to the spring seats, and portions are offset to resiliently grip the grid wires defining a selected spring seat above and below the grid and lock the head in place. The rectangular engagement of the spring components with the spring seats prevents rotation in their mountings.