This can be problem, especially as France is in the grip of a virulous outbreak of roundaboutism at the moment.
I tend to use larger scale michelin maps/atlases for my road navigation (infact I prefer the IGNs road maps too), and then get in close with the Blue IGNs.
Most of the new ones do have a grid on that should be compatible with most GPSs if you fiddle with the settings... (or take a compass!).