Not sure if they make it for the G43, but my favorite OWB holster for my G23 and G27 is the Glock Sport/Combat holster. It only weighs a couple ounces and is very thin. Holds the pistol very tight to the body. Only costs about 15 bucks, and you can get a spare mag holder too.
I don't recommend small of the back carry. It's impossible to draw when seated, and if you fall on your back you can hurt your spine. Massad Ayoob cautions against them.