First is the sweater vest, in a traditional style. This are a bit fitted, and can be solid or patterned. You have to be careful to get something ... hmm, how do I put this? Something NOT like the sweater vests I wore in junior high. Here are some ideas:
Brooklyn Industries 5 Points Cardigan - I imagine this with dark wash skinny jeans & black penny loafers.
Merona Drop-Shoulder Shawl-Collar Vest - I love the dark teal color & can see myself throwing this on over many a winter outfit. (Yes, we have winter here in AZ. It starts in about 6 more weeks.)
The other option is a menswear-inspired vest, usually fitted. And therein lies the problem for me. I'm not holding out a lot of hope, honestly. But for those of you with smaller chests, here are some great pieces.
Kohls Chaps Pin-Striped Vest - more masculine than others, but classic & sporty looking
Kohls Elle Pin-Striped Vest - I like the more feminine cut on this & the puffed pockets & gathered back. The grey is a nice alternative.