Swing swivels are there. I bought one set for mine, see the pic. This is basicly a 2 piece assembly, swivel to one side of the hole and attached by hex-screw from the other side. When tightened up the swivel does rotate, but doesn't move along the axis. They do offer the sling too, but it's not exactly my taste (not with carbine hooks). And bipod to the laser rail.
Now I see that in European market the G22 is offered in 4 colours (black, olive drab, carbon and desert) and 2 barrel lengths (regular 20' and longer 24')
Trigger job is mostly made by replacing the trigger bar. Adding width to the middle makes it less flexible, thus crispying it up. By making it longer the trigger travel gets better. One guy here made the bar 1 or 2 mm thicker (can't recall exactly) and 3 mm longer, said it improved the thing quite much. Also disabling that unnessesary mag safety should clear things up a little.
To make the thing left-handed you'd need to swap the extractor (extractor claw, spring and mounting pin) to the other side, whole receiver and bolt is ambi. The metal/plastic parts should be reversible, I have my doubts on the metal plate, though. Maybe it's safer to just buy the left-hand bolt and that metal plate?