Quality merino wool base layers are some of the best base layers on the market. Their natural hydrophobic and hygroscopic properties wick moisture away from the skin and evaporate it to the outside. Which is what a base layer supposed to do. Merino Wool fibers are ultra thin (ours are 17-18 microns) and are NOT itchy.
However, if your skin is sensitive we have a 2 ply synthetic/merino wool base layers. Checkout Merino 50 products in case of sensitive skin.