If you want to use mainly autoroute, then I would suggest going on the motorway towards Paris (not Reims) then at Senlis come off the autoroute and take the short cross-country route through Ermenonville then out on to the major route, then back towards Paris, but sweep around the East and South of Paris on the A104 - Francilienne (this is not the dreaded Peripherique). If you look on a map this takes you right down to Evry then go down the A6 just south of Nemours. Take the N7, which becomes the A77, down past Nevers, at Moulins go cross-country again (*but a good route) on the N9 through St Pourcaine and Gannat, then on to the A75 at the next junction. You'll have a small toll to pay to Clermont Ferrand, but from there it's free, except for the toll at Millau. It's a lovely route, with lots of variation in scenery, especially once you get to Senlis on the autoroute - from there on it changes regularly, so there's always something to see. It's also cheap. You can use Mappy.com, or Viamichelin to look at alternatives if you don't fancy this way. We've used it for lots of years, and it works for us.