That's gonna be tough ! I'd say anywhere near the sea won't be surrounded by countryside, will be very expensive (charged on a weekly basis) and it is getting a bit late to book (for the popular destinations).
My personal favorite is Cassis (right next to Marseille) but for countryside/scenery Moustiers Sainte Marie in the verdon canyon (nice lake), Valensole, Manosque, Forcalquier.
Personally, if i were going to do what you are saying, i'd get a place near Aix en Provence (assuming you have a car)
Live in Provence 1 to 2 months per year.