I am one of those folks who break out in a sweat, itching all over, at even the memory of the wool sweaters I was tortured by as a teenager. (Mom: "I bought you these lovely wool sweaters and you are going to wear them!") I remember a lovely lambswool sweater I was given my first year of college that I wore only once and gave away. Aargh!
That being said, I approached my first pair of merino wool socks about 6 years ago with great trepidation, but decided to try a pair. I not only never looked back, but went out and bought a whole bunch of Smartwool socks and ditched all my synthetics. (I now wear Smartwool socks around home, too, and have gotten rid of all cotton socks.) They are softer, feel dryer when still damp and actually dried faster than the Thorlo socks I'd been using. (I ran some laundry tests with air-drying on a warm, dry day.)
I then tried a Smartwool baselayer top. Again, no itching at all. However, i did some tests and found that the Patagucci Capilene 2 that I had been using actually absorbs far less moisture. Lightweight merino wool is also rather fragile, especially when used as a hiking shirt. Capilene wears a lot longer. Finally, in hot weather, the Capilene shirt feels cooler, although its construction (ventilation) may have a lot to do with this.
As a result, I prefer Capilene 2 base layers in cold weather, especially if it's below freezing when I use a vapor barrier at night. I also wear a Capilene 2 top as a hiking shirt. I do use a lightweight merino wool baselayer top as a lightweight midlayer under my windshirt or rain jacket. The wool may not be warmer but it feels that way!
I'm sure that some folks are more sensitive to wool than I am and just can't wear merino wool, either. But I do recommend giving it a try if you've found regular wool itchy in the past.
The Merino sheep is a wondrous animal (although quite ugly because of its numerous skin folds, which also make it difficult to shear). Although we now associate them with Australia and New Zealand, the breed was developed in Spain during the middle ages and can be traced back to the Phoenecians.
Baking soda in the wash water definitely helps remove the stink with any fabric. I also do 2 rinses to be sure I've removed any detergent residue. Also, when laundering either synthetic or wool base layers, be careful to avoid fabric softener, which really ruins the breathability and wickability of both synthetic and merino fabrics.
As with everything, the choice of baselayer fabric is definitely a YMMV issue!
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey