Hey Emma
I’ve done most of my research over the summer and looking on here and http://www.realself.com To be honest from what I found it depended on how much breast tissue u have to start with, how much elasticity in your breast like when pinched does it stretch 2cm plus, also how much of your ribs showed and how thin your skin was on your breast.
Most people who work out a lot tend to go for overs. You can get a natural look with either under or overs but I think it’s easier to achieve with unders and blends more but that’s just my opinion tbh.
Also look into the pros and cons for both of them in terms of breastfeeding, mammograms regarding what u may want in the future.
If i were you just have a look at the profiles pics and similar stats of girls on here for what your hoping to achieve and contact them to find out their surgeon and get a few more opinions as the ones you have received are all really varied.
I’m having 325cc unders due to my size and shape plus I want them to look really natural.
Hope that helps!