I wear nursing tanks instead of nursing bras. They are more comfy for me, and when I nurse in public you don't see all of my back or belly.
I wear them to sleep too.
I have Glamourmom tanks - they are pricey, but awesome!?
My favorite bras are from Bravado, so comfy since my boobs have grown so much - from a DD to a F.
I wear a nursing tank to bed sometimes or a more sports bra-ish nursing bra from Bravado. The bodysilk ones are my "day" bras.
I also use my old Bella Band during the day under my shirt so I'm not exposing my tummy when I'm trying to nurse, no one needs to see the flab!