Depends where you carry the backup and what you perceive yourself doing with it. If your threat profile is such that you're more likely to be in a sustained firefight and need to reach a backup gun to keep shooting, the PM9 with 7 rounds makes more sense than the J-frame with 5. (And, frankly, an 11-shot Glock 26 that can feed spare G19 mags on your person makes more sense than either).
If your threat assessment is such that it makes sense to have your hand on a small gun in a weak-side pocket or jacket pocket when making seemingly innocuous but potentially dangerous contacts with people in the PI/Bail Enforcement side of what you do, I'd go with a hammerless or shrouded-hammer J-frame. Its less-square profile clears the pocket faster, and in a coat pocket will allow you to fire through the pocket in an emergency without fear of malfunction. I'd rather have 5 shots right now than 7 to 11 shots a second from now, in a fast-breaking situation.
Threat assessment is up to the individual. In the end, it's always your choice. Since you ask, I carry the same 127 grain +P+ Winchester Ranger-Ts that you're using in your G19 when I carry the PM9, and the gun runs fine with them. Only testing YOUR gun in YOUR hand(s) will determine that for you.
Good luck and stay safe,