Your doctor can give prescription for special under garment they call a camisole. Made from cotton and cones with two adjustable pockets for the drains. I got them and they are so much more comfortable than the special bras. You must get camisole before bras for insurance to cover the cost.

They were wonderful. I had 2 sets because had 4 drains. Took the pockets off as the drains came out. I had the last one for a month so got lots of use out of them. And the shower ones that came with it made showers so much easier

I ordered drain holders from Amazon that were much more comfortable than the nail apron the hospital gave me. Also got a mastectomy pillow and front closure bras. I wore these thru all my fills

Hi Kate2
I had my mastectomy last May2021. To control your pain after surgery I recommend a block before surgery. You have to ask the surgeon and anesthesiologist ahead of time.
For clothing, wear blouse or jogging suit with opening on the front You will be given bra with velcro and drain bag in the hospital ( ask for extra bra). Pillow I used the maternity pillow (pregnant women use during pregnancy). This pillow will support and elevate your arms. I slept on my electric recliner for a week. It helps me get up without straining.
Exercises after will be given by the physical therapist before your discharge from the hospital.

Sending hugs and prayers for your speedy recovery.