The ornamental design for the flotation therapy device, as shown and described.
FIG. 1 is a top perspective view of the flotation therapy device incorporating my new design;
FIG. 2 is a sectional view taken on line 2—2 of FIG. 1. The broken line depiction of a person positioned on the flotation therapy device is for illustrative purposes only and forms no part of the claimed design.
FIG. 3 is an end view of the right end of the flotation therapy device as shown in FIG. 2; and,
FIG. 4 is an end view of the left end of the flotation therapy device as shown in FIG. 2.