I actually *do* tuck in my shirt. I also wear relatively body fitting clothes. My only "rule" around clothing is to make sure that the waistband on my pants and skirts don't sit on my stoma. Otherwise, I almost always have my bag "squished" by something that holds it firm against my body...if I'm wearing a loose dress or skirt, I'll either put on tights or boxer briefs to minimize flopping and any 'bulges' should my bag get too full.
I've not had a problem at all with skinny jeans or any other form of tight clothing. The only thing I don't wear is a body fitting dress.
My only suggestion would be to try wearing your shirt tucked in while you're at home and seeing how your body does with it. I always try out clothing I'm unsure about at home and walk around in it for a few hours before feeling confident enough in public. If the bag's going to bust, I'd rather it happens in the safety of my own home!
Good luck,
Kismet