Welcome pinkbubbles!
I'm 5' tall and weigh 121 lbs. I happen to be somewhat busty, too. The men's xsmall that I wore in classes was about the most uncomfortable thing I've ever worn. For that reason, I bought a BC very quickly after certification.
A friend ask me to reply to your thread because I'm about the same size, but I'll tell you that very few people on this board agree with me about the comfort of the BC that I chose.
I bought a Sherwood Luna and am very happy with it. I tried about 3 other kinds, and cannot comment on a lot that's out there. I am limited as to availability where I live. I like several things about the Luna. It floats me in a great position on the surface of the water. I think that's important for comfort and safety. It is so comfortable in the water that I hardly notice that I have it on. It has a chest strap that is removable if you don't like it. And the part of the BC that inflates in front (jacket style) is only at the bottom sides, and when it inflates, it expands away from the body so as not to squeeze you. Some small women really like the back flotation BCs becasue they don't expand in front at all, but I tried two different models of back flotation, and I didn't like either one's fit. They were the Genesis Athena, and the Scubapro women's model. (I think it was Scubapro) This one had a very uncomfortable cummerbun. I didn't try the Zeagle that Zagnut's wife uses, so I can't comment on that one, but I didn't really think the fitted front would fit me very well because of my relatively large breast size. And, I didn't think I'd like something else that tight on top of a wetsuit. I can't stand a lot of tight clothing because I have Fibromyalgia, and things like that are uncomfortable to my sore muscles and sensitive trigger points. I don't expect you will know what that means, but I've added it just for your consideration. I don't know if this helps you, but if you have any questions for me I'll be happy to try to answer them.