I'd have to say that I've learned from experience that I don't need as many sweaters as I once thought necessary. Just trying to live with what works in our wardrobes is usually the best place to start. Swapping or raiding a family member's sweater stash might be a good second possibility. :)
And then there is thrifting. I like to be able to do a sniff test...so thrift stores are "nice" for that option. Etsy + eBay are also good possibilities. Some of my favorite searches are sweater coat, cashmere, Pendleton, Eileen Fisher, Benetton, Cowichan, and Fisherman. This is a good place to use previous knowledge of quality brands...and use those as search words. Pay attention to fiber content + be ready to spend a little time hand washing or money dry-cleaning.
Keep cozy, friends!
All beautiful photos (+ sweaters) via links.