When layering with merino I've found it's best not to compress it anymore than you have to. Makes it less effective. Ex. Don't put on merino and then something like an Under Armour compression shirt over the top. I like merino, then lightweight hoodie, then a jacket that matches the weather. Usually hump in with the jacket attached to my pack. Pop it on when in stand. I also like the lightweight hoodies from FL and Sitka. Both will let you unzip for the hike in.