First good luck to you on this journey. I had a masectomy almost 2 years ago and glad I did. They did a nerve block while I was still asleep that helps pain wise. I didn't have to use heavy drugs for me it was not that painful.
The drain was in for a week and then slowly do the excersize they give you.
I had a big pillow that propped me up in bed and you will need zip up tops if you go with masectomy. I bought on Amazon some zip up hoodies that had pockets inside so you could place drain in pocket. I had an aggressive cancer so chose masectomy over lumpectomy. I use a prosthesis as at 69 did not want alot more surgeries. I have nice cotton ones and a silicone one I got thru Amazon. Thinking of you.