@Cath1 I had double mastectomy with one lymph node from each side removed in May (no breast reconstruction), movement of both arms was a bit limited but wasn't as bad as I expected right after surgery, but yes, button up shirts are definitely a good idea. I bought a few before my surgery.
It is important to see a physiotherapist specialised in breast cancer, who can help you with the right kind of exercise. I haven't done this and have been self-managing but am regretting it now. Even though I have mostly regained the full range of movement by now, I still experience some tightening of the chest area every now and then, and think I still have some cording issues and some swelling of the armpits, especially at night time. So, I have booked in to see one next week and hope to get a better understanding of my condition and what can be done. And so, will strongly recommend you to see a physiotherapist specialised in breast cancer to support you.
All the best <3