No sleeves, no problem. Vests are more versatile than you might think: layer a casual military style atop a sundress for added interest (and, more importantly, added pockets!) and choose a blazer-like version for the office to feel far more "dressed" without getting drenched in sweat.
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CARGO TWILL VEST, $139, VELVET BY GRAHAM & SPENCER, NORDSTROM.COM
Say what you will about sweater sets, but sometimes there's nothing better than a good cardigan. They're the easiest layer to stash in your bag, and the coziest to bundle around you later when you're shivering at your desk (who controls these things, anyways?!)
If you're looking for something with the casual cool factor of denim, the bomber is your new best friend. If you want to steer clear of anything that reminds you of the boys on high school varsity, pick a style in a femme fabric or one with a shrunken fit.