Hey laura,
I was told by my surgeon to stick with the cup size i wanted but go up one back size.
i.e i am hoping for 34d/dd and so at the moment i am wearing 36d, if that still feels tight then you can always go up another back size, then you may want to come down a cup size. I would suggest trying a 34d first then if that is no good try a 36c. hope this helps x x x