Hw much weight and volume you might lose in your breast is based entirely on how much fat you carry in that area. Like the rest of our bodies, our breasts are very individualized!
Seem lucky ladies will have say, 80% breast tissue and 20% fat. When they lose a significant amount of weight, there breasts will stay relatively the same size.
Unlucky ladies, like myself, have mostly fat tissue, and very little actual breast tissue. When I lost weight, it ALL came from my chest. And there is nothing that can change that, besides surgery. A good bra will work wonders under clothing, but naked...surgery or personal acceptance.
I lost sixty pounds and went from a 34D to a 32 A, then after surgery to a 32F.