Carefully choose muzzle direction
As with guns, try on several and - if possible- wear them for a while with the gun in place to make sure it isn't rubbing in a bad place or otherwise uncomfortable.
And for the sake of safety, I'd suggest one that holsters the gun muzzle down. The ones that point to the rear would make me nervous when drawing.. and the ones that point the muzzle straight up toward the armpit give me the screaming willies. In an emergency, a split second lapse of trigger control during the draw could do very, very nasty things with either of those.