Swimming is amazing, I went to my schools pool and I saw a difference in my arms in a few weeks. I would do different strokes where I used my arms more than my legs and then i also got a kickboard so I could just use my legs. A kickboard may be a good idea because you can do soo much with it and they are cheap. Have fun

You can do resistance training in the water too. Aside from pulling your own body weight through the water. The therapy pool I go to has water weights. They're actually super "floaty" barbells in several sizes. The biggest take considerable pulling to bring under or move under water.