Postpartum breast size

I am in a wedding in October and will be 3 months postpartum. I need to order my bridesmaid dress but am totally confused on what size to get. The dress seems forgiving in all areas, so I am really picking a size off the bust (sweetheart neckline). The dress is ordered online so I can't go to a store and speak with someone.  Those who have already had a baby, when did your breasts return to regular size, or did they? I plan to breastfeed, but probably not exclusively at that point.