Allison, I didn't know there was an actual allergic reaction to wool...thought it was just a result of pre Merino, scratchy, old school wool. My comisserations.
Silk should not be considered in this day and age, as it loses its structure when wet (sags), holds water much like cotton, and is slow to dry. Hypothermia city in the cold but very comfy in the heat. It was standard fare in the kits of 19th and early 20th century mountaineers (Mallory wore lots of silk). For a long time I used Terramar silk longjohns mostly to keep my sleeping bag clean, but now use SUL merino from BPL, both for this reason and as a base layer.
It seems I alternate between synthetic and merino depending on the length of the trip in order to manage the stink factor. I haven't yet tried capilene, so I still might become a convert to synthetic.