My new variation on the cardigan...

Is actually an old trick, made popular by all sorts of people, including Kurt Cobain. While normally I'm never without some sort of thin cardigan, now that it's warm I'm never without some sort of super-soft, washed-to-death oxford. It serves exactly the same purpose, but is lighter and cooler for summer. I've been wearing them buttoned low over tanktops and tucked into full-skirts, or open over a camisole or t-shirt. It's arguably warm enough now just to wear a tanktop on its own, but I hate being without at least two layers on top. I think J. Crew has the best options—I buy from the mens department online, where you can snag X-Smalls.