When does bra size stabilize?

becketts

DD is 2.5 weeks old. My milk came in quickly this time and I'm currently EPing (DD is a preemie) and working with a LC to slowly transition to more BFing and fewer bottles. I have nursing bras from my last pregnancy, but they are stretched out and in need of replacement. At this point, would it be safe to go and buy some more or do I need to wait longer to make sure the sizing is accurate?