Large breasts -- swimming and running after mastectomy?

I've recently been diagnosed with multi focal invasive ductal carcinoma and need to have my right breast removed. I don't think I'll go for reconstruction but am really grappling with being lopsided after mastectomy. I have large breasts and even before all of this have always had problems finding bras, especially for exercising. I am an avid runner and swimmer. How will this work for me having one breast and a prosthesis? Thanks so much for any thoughts and/or experience with this.