Harry, this is a tricky one, without really knowing what you and your better half like. Safely within your time restriction we've been to Florence & Sienna which were both stunning, especially Sienna which is a beautiful very old fashioned city. Around it are great places like Monteriggioni and San Gimignano, which are again old towns. Lots of opportunity to relax, meander, soak in the culture, good food, wine fairly chilled out but lot of stuff to see and do.
Also there's Carcassonne and Avignon in the south of France. Carcassonne again is a beautiful medieval walled city, much like Avignon, with lots of history, great food etc. Without knowing what you guys really like its difficult to suggest. I'm making a huge assumption that you probably want somewhere chilled, relaxing but also where you can go enjoy some food, culture, style etc when you feel like it.