I am married to a Thai and have a Thai bank account, live mainly in Australia but travel several months per year over there.
A Thai bank account is the best way to go and do "TT" transfers from your Oz bank, making sure that the transaction leaves here in Oz$ and hits Thailand as such where the transaction is finally done.
Do not transact to Thai Baht here locally no matter what method you choose and stay well away from Travelex.
BUT.......................
I don't think the OP is planning a longish trip anyway so the Thai account is not really feasible and for a foreigner travelling is not that easy to open anyway. They have become rather strict over there on just who can open an account and this differs with different banks.
AUDTravelers Cheques are widely accepted and attract a slightly better THB rate than AUD cash, but mathematics needs to be done as there is a small fee on each cheque cashed so get the highest denomination possible.
If you are not able to get your cheques commission free it may be better to simply take AUD cash, but if worried about security split amounts between cash and cheques.
Personally if I didn't have an account over there, I would use high denomination cheques purchased commission free here and load up my credit card here before travel to put it well into credit.
Another thing to watch with using Credit Cards (which are widely accepted and convenient) is to demand that the transaction is FULLY activated in THB.
There is a growing trend for some Thai banks to do the conversion to AUD at that end and your final outcome is not as good as letting the whole transaction happen in THB which is later converted to AUD by Visa Mastercard etc.
As well as keeping away from Travelex at this end, I would avoid taking any plastic card over there which needs to be fed into an ATM to obtain Thai cash. Anyone without a Thai bank account will do better with a mix of AUD cash and TC's.
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Don't understand the strange look of the link, but it seems to work!