There are a few essential sweaters every woman wants in her winter wardrobe (about six types). The one I love the most is the shawl collar cardigan ~ it's comfy, cozy, and (if chosen correctly) works perfectly with your cropped leather jacket for a bit of everyday edge!
Colors can vary but if you've got the usual suspects in terms of leather jackets (cognac, black, brown) then your best bet is a cool neutral like grey.
My favorite is pictured above (James Perse) but the ones below are just as fabulous and cover a range of price points and attitudes.