I highly recommend AsiaTourAdvisor
I can honestly say you will not go wrong with choosing AsiaTourAdvisor for your private (or group) trek. I did the 3N2D homestay option.
This means you will receive an authentic insight into the culture of a genuine tribe. This is not always possible with mass produced tours. You will also get better value for your money because there are no middle men. Your tour is 100% personalized and you will not feel like you are confined to a conveyor belt type trek.
With the local guide, then you can easily alter the itinerary upon your request at any time