I'm sorry to hear that you need this done.
You don't say if it is due to having Breast Cancer, or perhaps for prophylactic reasons.
The biggest difference could be if you are having axillary clearance of lymph glands. This may cause you to have more drains/drainage, lymphodema, and cording. Some of these things may alter your mobility/range of movement.
I originally (in 2020) had a single mastectomy with axillary clearance. I had 2 wound drains.
I found PJ's good. Mine buttoned up, but T shirt top would be ok. The drains come out between the top and bottom.
I consider myself lucky. I had good range of movement, from very early.
I was worried re how to brush my hair, style and blow dry. But these things were easier than I had expected. My surgeon did not want me to get the dressings wet. I became good at sponge washing my top and showering my bottom.
Make sure you do your exercises. Quite early I saw a Physiotherapist specialising in Lymphodema and Laser therapy.
I wanted to have my arm monitored for lymphodema. They did Laser, which is supposed to aid cording, healing and the seroma I had.
The drains are annoying while you have them, taking them with you to the toilet and anywhere else you go. Take a bag with you to put them in when walking around. Some hospitals provide them. A pillowcase will do. Or a dressing gown with large pockets.
This May I had a Latissimus Dorsi breast reconstruction, and a Prophylactic mastectomy ( with reduction ) to the other side
And bilateral tissue expanders. With this I had 6 wound drains. Pj's and a bag again.
Do you plan to stay flat? If you are having for prophylactic reasons, has immediate reconstruction been discussed.
I'm sure you will be ok. Ask plenty of questions. Write them down as you think of them.