In another post here I spoke of adding “na” to the end of sentences in Thai.
That extra phrase is polite, but for those determined to convince others of your cultural sensitivity it really only takes you halfway. For that you will need to add “krap” (for males) or “kah” (for females). Note this is fixed to your gender and is unrelated to the gender of the listener/s, so it never changes for you.
Illustrated by the quite possibly apocryphal story of the US Army Sergeant during the Vietnam War who began addressing his troops using “kah” at the sentence end, a habit learnt from the company he had been keeping at night and ensuring listening Thai soldiers could barely keep a straight face, this is important.
Again, like using “na”, I suggest you don’t overdo it. Less is certainly more and, for foreign males, an occasional “na krap” is almost certainly encourages a potential employer or conservative Thai partner that you would be good choice.