We stayed at Christmas Middle in St. Goar. Perfect town to stay in. Close to trains and boats. It's been a number of years since we were there but the owner was very nice and the apartment was just the right size. Located above a Christmas store and wine shop.
That's great. You will have so much fun. Our best day there was a bike ride along the Rhine. You can ride your bike down one side, visit lots of cute towns, take the ferry across and ride back.