Patagonia Thermal Shirt
Hard to beat a thermal base layer to keep the chills out.
I love this shirt, I’ve worn it to death. Mine is a patagonia mid-weight, looks like they no longer make that, so I linked to what I think the equivalent is - “Capilene 3″. They have some nice wool shirts also and I wonder how they would be.
Available from Patigonia for $50.