Go for the bag! I am smaller than you and use a 35B, and it makes me very happy! (and no one ever made any comments by saying the bag was too big).
I am obviously in the minority here, if I want a 30, I want a 30 not a 35. I am 5"4' and I feel that the 30"is perfect for me.
You are spending a lot of money why settle for a 35 when you want a 30?
Take it! 35 is a good size for your height. I have 35 b and I am 5'5" with same weight as you