The ornamental design for a lower bodysauna, as shown and described.
FIG. 1 is a perspective view of a lower body sauna showing my new design;
FIG. 2 is a side view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom view thereof.
The features shown in broken lines depict environmental structure only and form no part of the claimed design. Dashed boundary lines enclosing the broken line interior features in FIGS. 1 and 5 depict environmental structure only and form no part of the claimed design.