Chastity and orgasm denial discussion

Hi everyone! I’m not sure if this is the right place for this discussion, but I couldn’t locate a more specific forum. My partner and I are looking into chastity (it was my idea) and after doing plenty of homework, it seems like the Holy Trainer V2 is an excellent entry point device (though it’s on the pricier side). I believe my ring size is 45mm, but I’m still unsure about the tube dimensions. They come in 48mm and 60mm. Several sources suggest measuring when you are at your smallest. During daily activities, I usually measure around 3.5 inches, though that isn’t necessarily the minimum or even what I can achieve. I’ve also heard advice to choose smaller sizes if uncertain. A shorter cage means less space for mess while peeing and limits growth potential, right? Regardless, any guidance would be greatly appreciated. Thank you!