For day trips the maps published by Michelin (scale 1 to 200 000) are still the best. For Domaine de Sivas you will need map 77 and map 81. We are just on the edge. There are now also maps by Departement and other scales available.
For tourist information the map Préalpes du Sud, Buëch, Dévoluy, Durance by IGN (scale 1 to 60 000) is very nice.
People who really love details, for instance for walking or ATB trips will need maps from the Blue Series (scale 1 to 25 000) by IGN. For Domaine de Sivas you will need map 3338 OT. And depending on where you are going to walk, you need some other maps as well.