What I’ve used and each experience with testing for designers.
-Acrylic depending on yarn it can be soft, easy to work with. However it can stretch over time and it’s doesn’t breathe.
-Bamboo yarn I’ve only made one item with this yarn and it was more of a mesh top. So I can’t really comment on its breathability.I did find it a bit harder to hold tension with simply because of it’s feel. It’s held it’s shape fairly well.
-Wool blend I wear this pull over for colder days it’s nice it seems to hold its shape well. It’s a 20/80 blend less wool but still some breathability.
While I do like some acrylic yarns I personally like natural breathable yarn to make sweaters, blankets with.
I haven’t made a wearable in a bit but here’s a few I’d recommend looking into.
24/7 cotton, or any 100% cotton yarns, Merino Wool, linen yarn . Depending on your preference with texture and breathability as once it’s done will really make a difference as to how much you’ll wear it. Not all yarns are scratchy but some can be over time with washing others seem to soften too with washes. I hang dry all my wearables after wash just to keep its shape a bit better and to avoid shrinkage.