The thing is, a lot of your vertical shoulder rigs are going to add some retention and contortions that may make it harder to draw. Particularly if you've got any sort of moobs/belly to reach across.
here's one with some added retention
The flip side is, if you're low on moobs/belly, concealing a fullsize gun horizontally can be challenging. Even a Glock 19. That's part of the reason the original
Jackass rig hangs the gun with the muzzle pointing slightly up. That slight muzzle-up might make you feel better about things.
FWIW, if you do consider a shoulder rig, mags carried horizontal is *way* easier to access as well. IMO the
Miami Classic II is the way to go, if you can get over the flagging thing (that, as TGS mentions, isn't really an issue).
Absent that, I'd be looking at pocket carry with suspenders, provided your day-to-day dress code allows for it. If you're retired, i seem to see old guys with a wife beater, hawaiian style shirt, and suspenders between the two all the time. Black socks and shorts for the added grey man.