Congratulations on achieving your fitness goals. The loss of breast size and firmness you describe is not unusual after what you've gone through, and aesthetic breast surgery can help.www.expertplasticsurgeon.com/html/breast-lift-reduction.html
You would need an in-person consultation with an experienced breast surgeon to get an individualized opinion, but here are some general guidelines.
1. If the change you experienced has caused only the nipple to sag down, then lift might be limited to raising the nipple and areola (peri-areolar mastopexy - scar around the areola).
2. If the changes have caused looses skin or loose breast tissue overhang, then the lift should involve removal of looseness from the lower breast (vertical or inverted-T mastopexy, depending on degree).
3. If the changes have left you with little fullness in the upper pole of the breast, then you options include internal support sutures or a small implant. I would not suggest a large implant, as you will probably notice additional sagging.
Your breasts would not get smaller from a lift procedure, only better shaped. Future breast feeding or nipple sensation may be affected. Your surgeon, after the assessment, could tell you how extensive your procedure would be.