There's nothing that moms want more after having had their babies than to get back into their pre-pregnancy clothes. With that said, there are some very, very nice, comfortable, easy nursing clothing to wear that are not so obvious to the world that you are nursing. There are many that have a little flap. There are some that just are a little bit looser than others. In many cases, you can wear your own clothes, but just a size larger to be able to lift up, or you can buy something from a specialty breastfeeding store.
More importantly is that you have the proper bra. And in that case, you're going to want to be fitted properly. You're going to have fluctuations in breast size during your breastfeeding time, and you're going to need to be able to find a bra that's going to be appropriate for that. I highly recommend no underwire bras at all, because they can really contribute to clogged ducts. So finding a supportive bra . . . and there are many, many versions out there now. Bravado, L. MacPherson. There are so many really beautiful bras that you will be able to find that easily.
So it's not necessary to buy any particular breastfeeding clothes. But it does make things a little bit easier in the long run.