With the first, I had a couple of button front shirts & a dress that I wore a lot (had to, the shirts were my military uniform - but I nursed her at the day care in the baby room while wearing them). The rest of the time, I kept a cotton flannel baby blanket handy - either to protect my clothing while burping her, to cover her (she was born in the spring - by the time she got active enough to object to anything over her head, it was cool enough that she'd put up with it & she weaned in the spring when I ended up in the hospital with the flu for several days).
With the second, I was a stay at home mom, made special nursing clothes for going OUT in or used center front button items from my maternity wear - the nursing meant that I could use the extra room at chest level for a while. The patterns and instruction sheets on "how to" set up regular clothes had not been available ten years earlier - and would not have passed muster as allowable alternations to a military uniform, anyway!