I own and have worn many different pocket holsters (I pocket carry 100%) and I have found the best holster for me to be the High Noon pocket grabber.
I do use a GALCO Pro 158 or a DiSantis Nemesis when clothing dictates a lighter holster. All of my trousers and shorts have extended and reinforced right pocket.BTW, I have worn a Nemesis for some time and have never had a problem with losing it on sitting down. With the extended pocket, the trouser material closes over the grip.
IMHO, you have the perfect pocket gun (642) now spend some extra cash and set it up right.
I also recommend a light brushing around the crane (I use an electric shaver brush) and a dry bore swab or patch through cylinders and bore at least once a week. You will pick up some lint, regardless of what rig you have.
Pocket carry dictates the same commitment to rigging and care as OWB or IWB. For me, it is a method and system in itself, not a stopgap measure when I can't carry a cannon.