A good service department will consider your driving habits and probably just go with annual oil changes. To be honest, what you are doing is kinda hard on any engine, and I suspect your driving is mostly just puttering around town. If I may suggest, how about once a week just take the car for a little drive to a nearby town? Maybe take a friend for coffee/pie? That's what we did with my folks when they stopped driving except to the store or church. They wanted to keep a car, but dad understood (he was a retired Oldsmobile service manager) that just letting the car sit there was not good for the engine, so they would take about a 15-20 mile drive once a week.