I have an app, that lists all my scripts and medicine as well as my wife's, I only had to use it to show a doctor here what she was using. Customs have never bothered to check, we come and go twice a year
For a start you. will need your original birth certificate, it has a registration no, that will identify you on the national database. If one of your parents is Thai you are Thai. If not you may qualify depending on how old you are, as they changed the rules. Good Luck
I would ask your company to soften their stance a bit and offer to do a bit of training of local staff if they will second you for up to 3 months, and you won't ask for Per diem allowance for the work