Most Helpful Guy
I used to work at Hollister. If you say you usually wear small or xsmall, you should probably be safe with getting a small. Nothing wrong with going in and trying stuff on though, each store is completely different from one another. I think that girls clothes at Hollister are more to better fit size than height, meaning your weight(thin) should effect the size more than your height.
Then again, I am no girl so I don't know 100%, hopefully a girl can comment for you as well =)