Add Greek key trim from M Trimming (under a yard) to ready made curtains. Sew it on or even easier, glue it on! Copy this gorgeous look below, for example, with Ikea's pink linen Aina curtain a pair) and M's Greek Key trim in Pewter/Taupe.
I know you said no drapes.but this might look really chic and cozy with the same greek key from the pillow we got at mcnabb. Chinoiserie Chic: Navy Greek Key Trim - Going to do this to my living room curtains