Michelin or AA road atlas is a cheap way of getting maps for all of France.
Either way, you want 1:200 000 or better.
An easy test is to open it at the first page of mapping, which will be around Calais, probably. If you can see canals, Guines, and a whole load of little roads, that's good. If you just see the Autoroutes, Paris and Epernay, find something smaller scale.
But do get an up-to-date map. It's always confusing when your small lane is truncated by an unexpected motorway and a brand-new TGV line.