Mature Metal discussion

Hi everyone, I’m new here and could use some guidance. Right now I’m wearing a Holy Trainer 2 with the small ring (45mm). It fits perfectly and I have no complaints at all. My KH and I are really enjoying my chastity lifestyle though, so we’re thinking of upgrading to either a Queen’s Keep or a Jailbird. Since there isn’t much gap on the HT2—unless I’m mistaken—and it sits just right, what would you suggest for adding some space with an older metal model? Thanks in advance!