I use a Kapture Group sliding back that was specifically made for the Area Swiss RM3Di. It is pretty light weight and the ground glass is designed to accept a collapsible Hassy V loupe. The V loupe is not powerful enough to nail the focus, IMHO, so I do carry a small 15x loupe, but often I also check focus on the back. I also know my lenses by now, and rely a good deal on the numbering on the body.
Kapture Group is now out of business/retired, so you will need to find one on the used market.