Switzerland, Germany, France Itinerary suggestions?

I'm looking for some possible suggestions for the second half of a two week trip we'll be taking this fall. Right now our itinerary looks like this: Sept 27 - arrive Frankfurt in early morning, pick up rental car, drive to Alsace Sept 27 to 29 (2 nts) - Alsace (probably Riquewihr) Sept 29 to Oct 4 (5 nts) - Burgundy (apartment just outside Beaune) Oct 4 to Oct 9 (5 nts) - ??? Oct 9 - probably spend night in Heidelberg
Oct 10 - depart Frankfurt in the afternoon We will be traveling with our two children (2.5 yrs and 6 mos), so want to take it slow and easy. We prefer to stay in smaller villages or the countryside as opposed to cities. We're looking to make this a relaxing vacation so we would love to find a scenic area where we could come back to an apartment or hotel on a few of the days and relax on a balcony with a view while the kids napped but we would still like to be centrally located to a variety of 'sights' so we could make day-trips. We are open to spending all five nights in one location or splitting them up. We're considering several possibilities: Interlaken (although I'm having trouble find anything in out price range for this trip); splitting the five days between the Black Forest and Lake Constance; spending all five nights in the Lake Constance area; doing a long day of driving in the middle and spending the five nights in Bavaria (we love Bavaria and this will be the first of four recent trips that we may not visit the region). We haven't booked anything yet, so the whole itinerary is still flexible but we have found an apartment in Burgundy that we love and is available on the dates we are planning to be there. I'd love any thoughts or suggestions people might have for us. Thanks in advance. Chris