Some good advice here. I had exactly the same surgery that you are having, Mine was done on 5/15. Good luck! You can do this.
BIG, button down shirts are a must while you have the drains so take one to the hospital to come home in. If you can get a mastectomy camisole before the surgery that would be great. They hold the drains. I could not find one before my surgery so I had to McGyver one out of a T-shirt once I got home.
I would not bother to take any PJs or nightgowns because you will use their lovely gowns,
Let me give you a few other things to take. Chapstick, Lifesavers or small hard candies, a body spray scent that you absolutely love (it will lift your spirits).
I also wished I had taken a few throat lozenges because my throat was really sore after surgery from the tube.
As for bras after surgery, there are so many options. What I have found to be most comfortable for me with these pesky tissue expanders is the Genie Bra. I got mine 2 sizes larger than I normally wear and I can pull them up over my hips very easily. They also did not interfere with my drain holes. I got the one with the lightweight pads. I also was lucky enough to get a pair of "knitted knockers" that were made by some local ladies who donate them to the breast center I went to. They work GREAT when you stuff them into your Genie bra! The Ahh Bra is very similar to the Genie.
Good luck and best wishes.