Yes, avoid France from mid July to the end of August because that's when the French are "en vacances" and the roads, beaches, campsites and beauty spots are crowded. September would be perfect time to visit France and I would recommend you holiday in the Loire Valley. It has pretty scenery; it has quaint villages; it has magnificent chateaux; it has above average vineyards; in fact it has the lot.
The towns along the river are lovely to wander around from Angers (terrific chateau) in the west, via Saumur (chateau and home of the celebrated Cadre Noire show horses, the mushroom growing capital of France and home to a magnificent sparkling wine made by Akermann), Chinon (actually on the River Vienne - medieval castle linked with Richard I and Joan of Arc) The town itself is ancient, wonderful and the local wine is very good; Tours, excellent tourist town, Blois (chateau) to Orleans in the east.
Other chateaux to see (must) Chenonceau (beautiful) Azay-le-Rideau (in the middle of a lake) Chambord (the most grand of all) Cheverney (home of french hunting) and many others. The last time we visited the Loire Valley we stayed in Chambres d'Hotes (B & B's) which are of an unbelievably high standard (see AA Guide B & B in France) but we have also visited using a caravan (the campsite in Chinon is a favourite) and a trailer tent.