I have several short-sleeved wool jerseys and long-sleeved tops. My long-sleeved tops are merino wool, and as for itching, they vary. I have some that do itch a little bit, so I wear a sleeveless jersey under them. But others are great, very soft. And I'm usually more comfortable with a sleeveless jersey under my short-sleeved wool jerseys.

They do work very well in cool temperatures. The last few evenings have been about 10C - 12C, and I've been wearing a sleeveless jersey, a thin merino base layer, and a waterproof breathable jacket ... and I've been quite comfortable.

But for cold temperatures, I like doing a polypro layer, then a merino wool layer, and then a fleece if necessary. That combination has worked very well for me.

I have worn wool up to about 30C, but over 25C, it got hot and rather uncomfortable, so personally, I wouldn't recommend wool for hot temperatures.