Kinda depends on budget I think. Its hard to beat their light hoody for weight and versatility (unzip it when its warm/zip up and pull the hood over when its cool). They are also featherweight light so packing an extra in your pack is easy. Not sure of the altitudes youll be at, but a lightweight hoody, medium core zip (a size bigger to go over your hoody), and your jacket should get you through what you need. Ive tried their older merino in the past and always went back to first lite, but Im going to pick up sitkas new light merino from this year and give it a go (the weight and blended fabric has me intrigued). Just so you know, the heavy core stuff is pretty beefy. I dont know if there is an application for it in september if you have a puffy type jacket. If weight isnt a concern then it would be nice to wear to bed and in the morning around camp, but you would probably be shedding it as soon as you started getting active.
