Colette, I have both the grey cashmere cropped sweater and the navy cotton square crew in Small. (For comparison, I am usually a small/4 in JCrew tops.) I think the cashmere fits perfectly. If I ordered another cotton square sweater, I might order a Medium so that it fits more like the picture, with the sleeves extending over the hands. It's not quite as oversized on me as it is in the picture in part because I have very long arms. The Small works fine but looks less interesting. I hope this is helpful. And, by the way, I love both sweaters. They are cropped but not too cropped. Perfect length for me.
BTW, that Topshop wrap top you pinned is gorgeous. I will be in Chicago for work next week and plan to stop into Zara and Topshop and potentially Nordstrom too. Unfortunately I am not really looking for reds, but if I were, I would try that top - so lovely.