You sound teeny tiny Gigi! I'm 5'0 but, err, medium shaped, especially in the upper body/chest/shoulders. My fitted jean jackets are all from LOFT, a few seasons back, before the more relaxed/slightly oversized look came in style. Prior to LOFT, best luck I had was in the children's section of Old Navy or Gap, size children 14. My LOFT collection includes XS and Small petite, as my weight fluctuates, and I gain first in upper body/chest.
I also have one cropped denim jacket from WHBM in small petite, which I don't wear as often because it's ... cropped. Works only with dresses, not pants.
You say WHBM works for you? I have a friend who's my height but shaped different than me (more pear than inverted triangle), and weighs less. She's teeny tiny compared to me! She borrowed my WHBM leather jacket last Fall and it looked totally different on her than me, in truth I think it looked much better on her, even if it was loose in the shoulders. It had much more "cool factor" on her than me.
Ever since, I've been playing around with sizing up in jackets to get that "cool factor" affect myself, with mixed (mostly dismal) results, because length also increases proportionately.
