Getting an United Mileage Plus credit card is a good idea if they still have the promotion that gives you 30K ff miles for signing up. That's half a trip to Thailand.
60 baht annual fee, before the first renewal ask them to remove the fee and they will probably comply, if not cancel the card.
As for credit cards in general, if you can't afford to pay off your monthly balance in full, then you can't afford what you were going to purchase.