I am late to this conversation but I found myself nodding along with almost every poster -- even the ones who contradicted each other -- because that is the crapshoot that knitwear is! I sympathize, because I, too, need to wear it for more than half the year. Although in my current climate it is not quite as crucial and I can get away with fewer knits or thinner knits or cotton knits vs. wool or cashmere, and cotton is more durable, although it does tend to fade.
I have zero answers. The brand that works for me one year bombs the next.
I love merino...except when I hate it. (Yes, some merinos are scratchy and awful. Others are super fab and incredibly durable! How do you know if you are ordering online? Answer: you don't.)
Cashmere is so plush, so pretty, so huggable, so light, so warm, SO PILLY!!! Except for my husband's 50-year-old-and -still-going-strong cashmere t-neck from Scotland (that I stole, but rarely wear because it is too warm!). And I own a few cashmere sweaters that I love so much I will wear them despite pilling. The Pure Amici below did not pill its first year but has pilled some in the years since -- I just comb the pills as best I can and continue to wear because it is a brilliant shape and lovely colour on me and so versatile.
My Zella hoodie from last year's NAS is another example. I LOVE this sweater so much -- but it pilled like there was no tomorrow. I am hanging onto it to wear as loungewear this year but it is past its prime for real-life wear. More's the pity.
The Boden hoodie from last year worked out much better in terms of quality. I have also had surprising luck with some J. Crew sweaters, but the quality is extremely mixed. The best ones I've had are from the Collection line (on sale).
Cheap sweaters? Some are genius -- especially if cotton -- and some are a disaster. Take my beloved grey cardigan. It's a total mess, and was almost from the first time I wore it, but it is so useful I hang onto it until I find a replacement. That's fine for me, working from home, but not acceptable for you in your public-facing role. Argh!!!
I do try to wear my knits for at least 3 years if I can. But I'm about to do a big edit this fall. I'll be sad to see some of these go, but I really don't have a choice any more.
Good luck finding ones that meet your needs.