Go to a bank and ask about a prepaid visa card. Open an account with 100,000 baht and get a card with 100,000 baht limit. Each time you use it, the level drops.
Keep track of it on line. And transfer money when it gets to whatever level at which you start feeling uncomfortable. Want to buy airplane tickets for 300,000 baht, just pre-top up with 300,000 baht. Then use the card, buy the tickets, and you back to your 100,000 limit again.