I only have 36B boobs but there was still a slight difference after my milk had dried up. They went back to the same size, but they seemed a bit lower
I didn't breastfeed.. my daughter couldn't do it. She was tiny when she was born & couldn't get the hang of latching on properly. I pumped for about 2 weeks but I wasn't producing much milk & it really hurt so I stopped. She did just fine on formula.
I do think it's the pregnancy that has more effect on your boobies.. but if you don't want to breastfeed then that's entirely up to you. A couple of midwives made me feel like a bad mother for giving my daughter formula, which is totally out of order.