I totally used regular shirts. I just lifted them up or pulled them down. I also didn't use nursing bra's. I didn't like the way the made my boobs look. So I would just pull them down as well.
button down shirts and stretchy cotton/spandex shirts you can easily pull up or pull down to get to the boob. when going shopping for shirts, try it on and test it out and see if it allows for easy access to the boob(aka you can whip it out in seconds) if so, its a breastfeeding shirt lol