Well, I think it depends on how 3D you want your bun bun to be. Some people just make him as a sort of flat shape, some people give him a little nose and stuff, which would be more complicated.
has the same sort of body shape imo, you would just use the arm shape for the legs as well because Bunbun doesn't have feet, and give him a Bunbun face instead of a bear face, and his ears are the same sort of tube shape as his arms so you could use that same pattern piece again.
Bunbuns arms kind of stick out more to the side than those, but it was the closest to his body shape I found.
There's also another one here
if you wanted a simpler, flatter body shape, though her plushie came out very tall and skinny while Bunbun is more plump, so I would recommend fixing the body a little.