We claim the ornamental design for a convertible bed, as shown and described.
FIG. 1 is a top perspective view of a convertible bed of the present invention;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a first side view thereof;
FIG. 5 is a second side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a cross-section view taken along the line 7-7 of FIG. 2; and,
FIG. 8 is a top perspective view shown in an alternate position.
The broken line showing of convertible bed is included for the purpose of illustrating environment and forms no part of the claimed design. Additionally, the unevenly broken lines in the drawings define the limits of the claimed design.