The ornamental design for a top and bottomsurfaceunit of a mattress, as shown and described.
FIG. 1 is a top, rear and left side perspective view of a top and bottom
surface unit for a mattress according to the new design, the broken lines
showing the side are for illustrative purposes only and form no part of
the claimed design;
FIG. 2 is a top plan view of the top and bottom surface unit of a mattress
shown in FIG. 1; the opposite bottom plan view being a mirror image
thereof;
FIG. 3 is a left side elevational view of the top and bottom surface unit
of a mattress shown in FIG. 1; the opposite right elevational view being a
mirror image thereof. The broken lines showing the side are for
illustrative purposes only and form no part of the claimed design; and,
FIG. 4 is a front elevational side view of the top and bottom surface unit
of a mattress shown in FIG. 1; the opposite rear elevational view being a
mirror image thereof. The broken lines showing the front are for
illustrative purposes only and form no part of the claimed design.