Should you wear a bra when you sleep while breastfeeding?

I'm a new mother and my son is 2 months old. It seems that my left breast is bigger and produces more milk. I haven't been sleeping in a bra; just putting nursing pads in my shirts. He wakes about every 3-4 hours to nurse and when I roll over my breasts are very sore. I'm nervous that they will sag and was wondering if I should start to sleep with a bra on and what are the best ones to use? Thanks in advance.