I just had a baby. And I don't know about where you live, but around here, maternity stores are few and far between. And what they do have is either pricey, or the selection is extremely limited. Usually both.
Finding nursing pajamas is basically a lost cause. You can, of course wear regular pajamas and make them work, but nightgowns are out. And since I nurse pretty much all the time (I like to nurse past one year) that means I usually can't wear nightgowns. I've made myself a couple nightgowns, but I had a favorite one I'd bought during a brief not pregnant or nursing period (my oldest is 5 and I just had number 4). It has Eeyore all over. I mean, who doesn't love Eeyore. He's the perfect little morose donkey, who sometimes loses his tail. You, know, friends with Pooh Bear.
So, despite the fact that I'd had this nightgown for years, I'd only gotten to wear it a few times. After Little A was born, I added a placket so that it became a nursing nightgown, and now I can wear it to my hearts content. Even after I finish nursing, since it still functions as a nightgown for non-nursing persons. (Well, me.)
I added a placket to the front of the nightgown. I did this the same way I've learned to do continuous laps when sewing sleeves. I topstitched it down to finish it, and handsewed on some snaps. You could also use this method for any shirt you want to make a nursing top; just make sure that there is enough ease that the shirt wouldn't pull too much when closed.