Forget learning the language for a short period (advice from someone who speaks 6 other languages and has a Thai wife ). English will do you just fine. Just learn few phrases, like Hi, Thank you ...

Chai = yes. Can also use "Krap" (meaning "OK" if you are male), "Ka" if female.
Mai = no

If you are male:
Sawadee krap (Hi)
Khob khun na krap (Thank you)
Yindee krap (You are welcome)

female:
Sawadee ka (Hi)
Khob khun na ka(Thank you)
Yindee ka (You are welcome)