The sole FIGURE is an isometric view of a front, top, and right side of an ornamental design for a mattress.
It is understood that the dash-dash-dash broken lines represent a pattern on the surface of the mattress or environmental structure that form no part of the claimed design. The dash-dot-dash broken lines on the mattress of the sole FIGURE depict a mattress with a symbolic break in its length and width. The appearance of any portion of the article between the break lines forms no part of the claimed design.