I like to wear coats year-round, even in the summer, if it's not too desperately hot. Like a bed comforter at night, there's something assuring about having that outer layer — especially if, say, a gust of wind wants to have a go at your skirt — and it can completely change the tone of an otherwise casual outfit.
While searching for a spring-weight sleeveless coat, I stumbled across this knee-length gray option from Zara. Its long, lean lines and raised lapel collar instantly dress up a t-shirt and cropped pant, and its lightweight softness — it's cotton-blend, unlined, with just a bit of stretch — makes it as comfortable and easy to wear as a cardigan.
Zara "velour" coat, $129, available at Zara.