For a more specific suggestion for a route that does not involve big mountains, I once started a trip from Charles de Gaulle airport and rode south to the Pyrenees to join friends on a supported tour. I headed generally southwest from Paris on country roads to Chartres. I crossed the Loire just west of Orleans. From there on south, a bit west of Chateauroux continuing through the Perigord region south of Limoge and crossing the Dordogne River at Domme just below Sarlat. Anywhere from there you could pick a gorgeous route more southeasterly to Marseille, hilly but avoiding the heart of the Central Massif. I continued south to the Pyrenees.
I chose my specific route by linking up the smaller "D" routes on the Michelin maps and avoiding the larger "N" routes in red. It was country roads the whole way with just an occasional connection on an "N" route. A large scale map of the country supplemental to the detailed maps is handy to see the big picture of your overall direction of travel.