Same here. I keep a reasonable THB balance in my Wise account, converted obviously from my GBP balance. When the rate is up a bit, I convert, or an automatic conversion can be set up to take effect if the GBP/THB reaches a pre-determined level. And come the end of the month make sure there is sufficient THB to transfer for Mr IO.
The Wise card is very good, in that, if you do say a USD transaction and there is insufficient USD in your balance, they will automatically top up the USDs from your GBP account, at the current going rate, immediately, in order to fulfil the purchase.
Cannot fault Wise at all.