I'm too big to get away without some decent support (DDD/G cup). I plan on layering with tank tops as I'm almost positive a nursing tank that would accomodate my breasts *and* fit my plus-sized body does not exist. Since my cup size is so large, I'm going to convert some of my non-underwire bras and tank tops to nursing bras/tanks using the directions
here, since there are like 3 styles of nursing bras that come in my cup and band size and they are really expensive and I have yet to find a 2x nursing tank. I do have a few bravado bras and two regular nursing bras to see me through the first few weeks, but as I plan to be mostly at home anyway I'll probably just go without. If you want to layer without the pain of cutting slits in tank or paying the money for Bella Bands, you can always try out
The Belly Hugger. I've heard tell they don't work well for maternity use, but as a cover for your belly while nursing I would think they'd work better and with their clearance prices I know I can't make them myself for that cheap.