I would fit sheathing on the outside only, then a breathable membrane then vertical battens then your cladding (assuming horizontal cladding).
The general public underestimate how strong timber is, I once lived in a brand new house of which it's walls were 25×50 studs (end on yes end on) with a layer of 12mm PB each side, so the wall thickness was only 50mm, all pretty solid, I never would have believed it but I 'visited' other parts of the estate that were still under construction after I'd moved in so that I could see how my house had been built.