I had only one breast removed (and several lymph nodes) but I had excellent mobility from the start. Two breasts is more likely to cause an impact on your mobility for a while, as will reconstruction if you are having that immediately. If you can, it’s good to plan for some anticipated difficulty as the results vary immensely depending on breast size, extent of surgery, your own healing rate and accommodation of discomfort. Some people have difficulty in raising their arms above shoulder height, and will
be encouraged not to do so for some time to avoid undue strain. If you have a better outcome, wonderful. As they say, plan for the worst and hope for the best. Either way, it’s finite and best of all, surgery’s done! Best wishes.