Open a bank account in Thailand.(with ATM and internet possibility).
Make (regular) transfers from your home country account to your Thai account.
Atm withdraw (up till 30.000 baht a time) is cost free.
Coming to Thailand,have some small money with you (taxi costs) and use the ATM's at a bank as soon as possible.
Exchange rates are changing from day to day,so I would not worry too much.