I breast fed both my kids for over a year and when I was done the ladies looked pretty much the same as they did before I got pregnant. I credit wearing a good fitting bra 24 hours a day. the girls need support.
I am a 36 DD still after losing some weight. I have noticed mine are sagging. I agree with the need of a good bra comment to keep the girls up where they belong.
The loose skin may firm up, mine did! Is it still a little wrinkly? Yes. Do i have saggy boobs in my mid 20s never having had kids or anything? Yes! But as has been said, a good bra fixes all ills! I promise! Will the southward point ever turn west? I doubt it. As a heads up I went from a 44J to 34E.
I wouldnt describe a D cup as being that big but I think to answer your question,bench presses,pushups and lat flyes will help firm up your chest region.
I am barely an A cup. I would be thrilled with even B. I would consider a D cup to be well endowed. Everything is relative.
Mine are quite a bit softer and wrinke up too. No firming up of the skin yet. But a well-fitting bra will make a world of difference (and yes even for you smaller ladies too!!!). Remember that something like 80-90% of the support comes from the band so a tight band is absolutely necessary! I know many like to wait to buy bras until they hit goal but buying a well-ftting bra NOW can help alleviate back pain, help your posture, and help fight the effects of gravity. I'd suggest starting with band size=underbust and then check for signs of proper fit from there.
FWIW, I'm a 28J and have pretty much no natural firmness but I can get great uplift and support with a well-fitting bra, as you can see here (pictures of me are at the bottom of the post).
I can flex my boobs too, AND my boobs have always been pointed downwards. No saggy, but pendulous. DDD, although after reading a few posts here I KNOW I'm wearing the wrong bra, so I'm probably F or something like that. I hate them, always did, always will. I'm going to have a breast reduction/lift after I lose the weight.
I also don't understandusing the numbers to describe breast size. Don't those numbers only relate to the band?? so a 44 person might have smaller breasts than a 32 person, just a bigger rib cage, whereas cups size is well.. cupsize???
Yes, that is how the band is described. Cups are assigned their (quite arbitrary) letters based on the differential between the cup and band size measurements, but the volume of the cups varies quite a bit relating to band size as well, because of how wide or narrow the cup is (a 40B is going to have more fabric in the cup than a 28B, just by the geometry of the chest).
One breast "Lil Miss Perky" firmed back up and can stare anyone in the eye. My other breast, "Ms. Mopes-A-Lot" has always been the larger sibling and as such, always had a harder time looking people in the eye. She's pointing south. Even with the shrinkage from 44DD to 36C, she likes to pancake flat and list to the side when I lay down. I'm really okay with that. Anyone who gives me grief about these gals can forget about ever being blessed with their charms.
But on a purely aesthetic note, I found a well fitting bra makes a ton of difference in the clothing front. Where I hated wearing a bra a hundred odd pounds ago, I practically bathe in mine these days just because they are finally that comfortable.
Oh good for you ladies.
Mine have firmed up and have become perky. I am 60 years old and my breasts are 25 years old. I hate it. I exercise a lot, that may be the reason. I would love to have "grand mom" breast.
I'd suggest starting with band size=underbust and then check for signs of proper fit from there. 
