Me and my girlfriend like the occasional bit of bondage role play. We don't have a D/s relationship just like to fool around. My girlfriend like to do a lot of tease and denial with me and like the use of cock rings and similar toys but we always find that my cock swells massively and one vein in particular literally looks like it is about to explode. We've tried a few different types and I can't find anywhere that there are specific sizes. Is there anyway to tell which ones to use?