My partner and I are doing a couple of small christmas things so we've been looking at seasonal stuff that doesn't require a full choir to sound really good. A lot of christmas tunes I like better when sung with a choir. However, we're doing God Rest You Merry Gentlemen as a waltz, which actually sounds quite nice, (we dropped the Russian version where you emphasize the beat between lines with a loud basso "HEY!"). One song I love is Maddy Prior's Long Shadows, its a winter song and very nice. There's a gentle song in the Oxford Books of Carols called Men from the Fields, well suited for single voice and any instrument that can carry the chords to it. A local group likes to do Good King Wencelas and head straight into Red Wing on the fiddle.