Every time when winter comes, most Thailand's people will plan to travel at popular Thailand national parks but you may still experience a lot of people and lack of peace. I recommended you travel to Thailand Wildlife Sanctuary instead of national parks.
I recommended you to travel at Phu Luang Wildlife Sanctuary, which is very quiet. It located next to the Phu Ruea National Park and about 35 k.m.
The Phu Luang wildlife Sanctuary was established in December 18, 1974. The highest mountain, which peaks at 1571 m. and the Phu Luang means a large mountain or the Mountain of the King. Best time to travel is between November and January, the temperature highly drops during the winter to 0-16 °C