FIG. 1 is a front perspective view of a mattress in accordance with the present design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a front view thereof; and,
FIG. 7 is a rear view thereof.
The dashed lines in the figures form a part of the claimed design.