Well if you are making a sweater to be warm for winter then I would get "super wash wool" (won't shrink). But if its for warmer weather then an acrylic blend would be fine. I would get baby yarn as its normally softer than other brands, unless you want the more expensive kind. 
I am not an expert, just knit and crochet a bit when I have the time.
I am not an expert, just knit and crochet a bit when I have the time.