Well, I started out small (A or B cup) and was only a C when nursing, and I found the basic bravado bras were great because they stretched to fit while everything was adjusting itself, and they also accomodated the sort of regular shifting of full / empty breasts. I bought new ones once things settled down.
I did use nursing shirts, because ds wanted to nurse almost constantly (like, we couldn't get through a 40 min trip to the grocery store without having to stop in the middle to nurse, otherwise there would be a screaming fit and he screamed like the world was coming to an end) and I have a long torso and high breasts and like low rise pants, so the whole discreetly whipping out the boob from under a loose t-shirt didn't work for me because they didn't hang low enough for that and I would end up with about a foot of exposed skin.
I liked the Glamour mom tanks because I could wear them as camisoles under things in winter and by themselves in summer, and also I got a "boob" shirt (you can get them at www.milkface.com)
, which I wouldn't really wear by itself, because it was clingy and it took me a long time to loose my baby weight, but it was super easy accesss, especially when nursing in a sling. I tried some other nursing shirts, but I have a long torso, and most of them hiked up. Also, I found that anything where I had to pull a layer up to get to a slit, etc, was way too complicated,a nd the fabric would stick together and you would end up pulling up both layers, or spend 5 min sorting yourself out (because of course you then have to undo your bra while your hand is fishing between two layers of fabric) before you could actually get the baby to the boob. Which didn't end up being all that discreet.
The other thing I did in the winter to keep warm, was I bought a lycra long underwear shirt and cut the chest out of it, so it had a full back and the part left that covered my tummy. I wore it under regular cotton t-shirts that weren't too tight, and it was pretty warm and easy to use.