Does anyone know of a driver who'd take my wife and I from Chiang Mai to Chiang Rai in a modern, comfortable car with air conditioning on 12 September please?
I don't know any driver personally. But Chiang Mai is touristy city. You can ask the information at the car-rental counters at the airport or the tour desk at your hotel.
Chiang Mai to Chiang Rai is around 200 km, not over 3-hours drive.
Have a nice trip!