You could ask around at New City Sukhothai.
My wife has a unfurnished studio flat 1 of 3 that is coming available.
Its in a good location about 1 kilo out of Muang Kao old city Sukhothai near Wat Sri Chum.
No air-con at the moment but I could ask the Mrs to arrange if a long stay.
3000 per month 40 sq metres living and a back yard area.