Merino Wool Base Layers:
Sheep Run Chocorua Midweight Crew 

100% 18.5 Micron Merino Wool 230 g/m2 Interlock knit construction 

This is similar to the Minus33 Men's Chocorua Midweight Crew.

One of our favourite Amazon reviews (by Mark Dalpiaz): I bought one of these a couple years ago and absolutely love it. It takes the place of a full on sweater with a fraction of the weight and volume. I live in coastal British Columbia and the weather can go from blazing hot to near freezing rain in 30 seconds and it seems like I am constantly getting splashed with water (either in the boat, kayaking or just feeding cattle). Under these conditions, wool is king. This shirt is perfect for layering and so comfortable and versatile it's amazing - throw this over a t-shirt, top it with a fleece jacket and a raincoat and you're good from the Baja to the Arctic. I am just getting ready to take it on a 3 month trip through Chile and Argentina and it is so comfortable that it literally has replaced a whole collection of Pendleton shirts (sorry Pendleton, but I hardly wear you anymore since I got this - talk about freeing up space in my luggage!). I also bought a couple of the lighter weight wool tops at the same time and they are all very high quality, very well made and super warm. I'm kind of a relic as I grew up on wool and never did make the switch to synthetics. I've always thought synthetics were were cold as all get out, uncomfortably clammy, totally overhyped and they always smell like some sort of toxic petroleum byproduct. Synthetic clothing is something that manufacturers wish people liked because it is cheap to make and old pop bottles are pretty available (basically free, we throw more in the ocean then we reuse), but humans are kind of a funny animal and we're hard to fool. Even after 30 years of pushing coal tar based plastic garments on people there are still millions of us Luddites haunting second hand and army surplus stores looking for high quality wool clothing. I guess somebody must have noticed because now it's available brand new at Amazon. Too cool! Have things gone full circle or what? I've got to try those crazy Minus33 wool t-shirts next, they look wonderful.

Oh, and about the cost. For what you get, these things are dirt cheap. These will outlast any number of spun coal tar units. And, real people make them, real people grow the sheep, real people shear the sheep and, after treasuring them for years, when you finally do wear them out you can compost them and use them to grow vegetables. What more do you want?