Do you have a front loading or top loading washer? I have thrifted regular wool, merino wool, cashmere, and various wool blend sweaters and I always wash them on the handwash cycle on my front loader and then lay them flat to dry. I wash all my woven wool skirts on the same cycle but hang them to dry since they're not knits. I never have problems: in fact sometimes I deliberately try to felt things for crafting and it seems to take ages. I do come across felted sweaters in thrift stores though so others aren't as fortunate!
I do take certain precautions: I only wash them with other delicates so that there's nothing bulky (like jeans) to cause agitation. When I transfer them from the washer to the flat surface I support all of it so nothing hangs down and can sag out of shape. And I don't wash them very frequently: instead at night when I take a sweater off I hang it inside out from a hook over my closet door and let it air out. In the morning I do the sniff test and almost all of the time it still smells clean (and I do sweat under my arms). I've read that wool is antimicrobial although I'm not sure if science backs that up or if it's more of a marketing thing. I just know I don't need to wash my woolens very frequently and I have a sensitive sense of smell!
The softer the wool the more likely it is to pill, because the fibers are shorter. But most of my thrifted sweaters have very minimal to no pilling, so perhaps once you de-pill once you're set? I did thrift a tags-still-on cashmere sweater that I wear as pjs and it's pilled a lot, but I haven't bothered de-pilling and seeing if it happens again.
My mom finds almost all wool itchy, including cashmere and merino. She's had better luck with 100% alpaca, but I'm not sure how common that would be as a sweater in retail! And when I knit a pair of socks out of 'superwash merino' (chemically treated so it can go in washer & dryer like smartwool socks, which changes the fiber's structure), she didn't find those itchy at all. So Smartwool or Ibex or a line like that might be your best bet.
I hope that helps! I really love wool and find it fascinating, but I'm also fortunate in that it doesn't make me itch.