I want to support my ostomy bag while I walk on a treadmill, but I don't want it to confine or cause
any back up to the wafer and cause a leak. My shorts are snug, but are an expandable fabric. "Yes, I find that compression gives output little room to fill the bag, so it will often push it back towards the wafer and cause a leak, like you’ve experienced."
Do you have any suggestions?

I have had my illeostomy for 50 years. I have never had a leak when going to the gym. Maybe it's because I don't wear tight shorts. I just wear loose shorts. Give it a try.

My daughter is getting married in Dec and I am looking for a dress that will hide my Ostomy appliance. These suggestions are fantastic.My device is high, a little above belly button and my flange bulges out when I sit. Any suggestions?

Congratulations to your daughter, Claire!

Are you working with a seamstress to get your dress fitted? If so, this would be something to bring to their attention, as I'm sure they have creative ways to give your appliance support and concealment without needing to use other products.

However, if that's not an option, have you considered any stoma wraps or even support belts (i.e. StealthBelt)? Their success does often depend on how quickly and how fully your bag fills, but generally speaking, they can help to flatten things up front.