Volunteer work in Thailand

Hey everybody!
I have been planning for a while to go to Thailand next year February in my semester break to do work as a volunteer in a school and to teach English there to Thai kids.
I came across the idea a few months ago when I was studying brochures on opportunities to spend time abroad. The mimimun stay is 8 weeks which I thought would work out with my semester break which is usually 10 weeks. But today i saw that unfortunately those holidays are "only" 7 weeks long. But I dont want this to stand in my way and to keep me from going to Thailand.
I think it would be a good experience, especially as I want to become a teacher but have not gathered any experiences in this area so far. And Thailand to me is a thrill. A completely different culture, language and lifestyle.
I wouldlike to ask you if anybody is familiar with this topic and can give me a bit advice. I am still looking for the best company to go with. The best one so far is www.travelworks.de, they would also offer me a 6 weeks stay even if 8 weeks is their minimum as they say in their brochure. This is really kind of them.
But still I am looking for other companies so I can compare them to each other and decide then which offers are best for my needs.
I am grateful for any help on this. DANKE