I'm not to familiar with Chang Mai, but Bangkok is the sex massage and freelancer/escort capital of the world. If you want the hottest full service massage girls, I would recommend checking Sukhumvit Soi 22, 23, 24 massage shops. All shops have a menu that you can choose from like Nuru, Oil, etc and all are full service, no upselling + extras like the BS the massage shops here try to do. Escort wise, Agency's I would avoid as it's higher fees for mediocre services. The best I found is finding independent escorts though dating apps like Thai Friendly which is free to sign up as you will find tons of girls there of all ages looking for short time for some bhat.