Interestingly, the texture and shape changes in breasts that are attributed to nursing are actually the result of pregnancy. Whether the mom never nurses, or nurses for 25 years, the changes that pregnancy brings will be the same (for that mom -- mom's bodies vary quite remarkably, and some mothers of many children have perky B cups at 80 while other women who were only ever pregnant once for a couple of months may sag tremendously by 25).
Your breasts will keep changing, though, over the coming years - they are sensitive to the hormones of your cycle, and will be fuller and perkier at some points in the month and softer or saggier at other times.
Unless your weight changes a lot, your breasts will end up being pretty close to their original cup size (although the band of your bra will go up, and cups are proportional, not stable, so you may need a bra size that is a cup or 2 smaller to compensate for your larger rib cage measure -- mom's hearts grow during pregnancy!)
That means if you're buying a larger band size, but the same cup size as before, you're getting the wrong size bra -- without your actual breast size changing at all.
On the happy side, though, the softer, less-dense breasts of the post-partum woman are less likely to get pre-menopausal cancer and lumps of all kinds are easier to detect than in firmer, denser breasts of the never-pregnant... There had to be some perks other than the super-cute baby, eh?