Nursing Bras

Hello ladies! I have two questions for all of you.

First, I read I would want a nursing bra to sleep in. Why is this?🤨

Second, I am in search of a good but hopefully inexpensive nursing bra or two. My problem is I am tiny. Like. Ridiculously tiny all the way around. I would need something in tje 30-32 range, possibly a size C (I finally had bought a B for the first time ever, and now I feel like I don't fit it as well. So crazy!) Does anyone have good recommendations of where to shop? Looking through Google is overwhelming...😓

Thank you many times in advance!!