Every single time I buy a "water-proof" "breathable" jacket it turns out it's neither.
Meanwhile I've hiked in a constant rain for 5 hours wearing a traditional wool sweater and the water didn't get through. Felt a lot nicer than wearing plastic, too.
In a test I did, my dad's old leather jacket is more water-proof than a modern hardshell I still own.

So basically, I'm set for the upper body, with wool or leather depending on the temperature, and a merino base layer. Only thing I'm struggling with is finding a solution for the legs, using natural fiber.
Cotton is shit. Leather pants are gay. Any ideas? What did the pioneers wear? Should I try out tweed?