I've now purchased a few nursing bras. It seems early as my boobs haven't actually changed size, but my ribs are definitely shifting a bit wider and some of my regular bras feel like they're cutting into me by the end of the day. The two I bought today do not have underwire and are more of a stretchy fabric. They're designed to 'grow with you' or so they proclaim. I went with the one that was for 40C (and a few other larger cups) (rather than my normal 38C) since I'm already feeling the need for something larger around my ribs. Since I'm going to need to get use to sleeping in something, or so I'm told, these seem like they'd be pretty comfortable and up to the task. It was so odd and foreign to buy bras that didn't come from Victoria's Secret.
It's pretty wrong that this seems like one of the strangest baby-related purchases that needed to be made.