Hey, challenging situation! You’re definitely on the right track, thinking about PA12 and copolymer blends for living hinges. They’re notoriously tough to pull off with 3D printing, especially when using materials that aren’t naturally rubbery or when the hinge geometry isn’t dialed in perfectly.

PA12 is actually one of the best nylons for this kind of application — it’s more ductile than PA6 and has great fatigue resistance. I’ve personally had success printing living hinges with PA12-CF blends (carbon fiber adds stiffness but surprisingly doesn’t kill flexibility if the hinge is designed properly). Another solid choice is PA11, which is slightly more flexible than PA12 and handles repeated bending better. Some SLS prints in PA11 have survived 500+ cycles in hinge tests.