Chastity and orgasm denial discussion

I’m talking about the physical devices here. I own an MM Jailbird and while the length feels right, I think it needs to be narrowed by around a quarter of an inch—perhaps exactly 5mm. I might also manage to shorten the length by that same amount. It fits well overall, although when I get hard, my erection pushes it down slightly, causing some swelling at the base. I’m looking for something that provides a genuine feeling of tightness, but those quality options don’t come cheap! My concern is buying another one and having some dimension be too small this time. I know I can trim the width on my current model, and when soft, it will work fine with a slightly shorter length. Do smaller devices perform better?