Urban threads has a pack called pocket monsters. Design number UTP1647. These designs have the pocket digitized with the animal. Worth a look.

Designs By Sick has a cute set of Animal Pocket Toppers which includes a cat. In search box type animal and go thru sets til above set comes up.

SQ

Any design you want to put in a pocket - Pin the center of the pocket down about 3/4". Then put pins near the outside edges so that it makes a very shallow U or smile. Next, hoop. Move design to top edge of pocket and check by running your rectangle frame. If that fits, try bumping your design down into the pocket two or three bumps, then run the frame again to be sure stitches will fit. May want to slow your machine down a bit, too. Once you do one, you'll be hooked! Have fun.