My "user case" that goes on whatever Barnack is in my kit on a given day, is the bottom half from a Leica IIIg case. ( They have metal strap loops riveted to the ends of the case, and will take a modern wide-strap)
KEH has decent prices on OEM leica cases.
You can also find Leica "half-cases" on e-bay for cheap.
The Luigi cases look stunning, but are beyond my means.
If using an old case, make sure the straps are new; the old ones get brittle and break unexpectedly.
I do not like using cameras "naked"; mine tend to get banged-up that way.
Regards,
Luddite Frank