Southern Yunnan is in China.
Lao Airlines  flies from Wattay International Airport (IATA: JHG, ICAO: ZPJH) to Xishuangbanna Gasa Airport (IATA: JHG, ICAO: ZPJH) twice a week (Fridays and Sundays).
Trekking in southern Xishuangbanna. There are a number of cafes in Jinghong where you can meet up with guides who will take you on treks to see old Dai and Bulan villages in Southern Yunnan. Cost varies, but plan on about RMB300 per person for a four day trek.
The treks are pretty easy, since you will be staying in villager's homes every night along the trail. There's no need to camp, and the terrain you'll be hiking over is hilly, but not mountainous.