I'd have to say... hmm. That's a toughie.
Probably some kind of rodent would be appropriate. My build is small (not slim, just small), and I tend to be really sort of timid and shrink away. A mouse seems very much like me, to be honest. They're also considered kind of cute, and well... a few people I've spoken to seem to think I'm kind of tiny and cute for some bizarre reason. Oh oh oh! And I really like the Burmecians from Final Fantasy IX too (they're rat people) and think it'd be cool to be one of them as well.