https://www.zontadistrict23.org.au/what-we-do/service-projects/zonta-breast-care-cushions/I was provided with a Zonta gift pack in hospital by my breast care nurse. A bag for xrays, a bag for the drain and a breast cushion. Cushion was a great help for the car trip home.
In the hospital I would have a large scarf around my shoulders/chest to hide my drain bag as I would go for a walk around the ward.
Link above for you to enquire if they're not available in the hospital setting.
My hospital stay was until the drain was to come out. Mastectomy was fine, armpit took time to settle.
Also, Knitted Knockers to be considered if you're staying flat
https://www.knittedknockers.org/Best wishes @CathL