Hi there, I don't have any advice on size and keeping an ostomy dry; however, I felt the same about swimming and getting into a jacuzzi. After several years of avoiding it for all the reasons a person with an ostomy worries about, I just did it. I put on a tank top and a skort and went swimming. It was wonderful. If you have to change your pouch right after because it's wet or maybe leaked under the seal but not into the water, so be it! As long as you're not having your pouch leak where it would contaminate the pool, you are fine. After that experience, I continue to swim and go into spas with friends. Our pouching systems can work okay for swimming. Make sure it's secure before, and if you feel the activity may require you to change it after, it's all worth the wonderful feeling of swimming and getting the exercise we all need. Best of luck to you, and remember, you can do anything you used to. Just make that first step.