Get a Wise Card and put Thai Baht on it and then you can withdraw and use it in shops. Still have to pay 220 baht to withdraw as Thailand doesn't yet have Wise in their country. If you withdraw using your own country card, press no when it asks if you would like to accept the exchange rate and you'll get closer to market rate rather than what the banks want.
A quick google search in your area for an ATK provider for travel purposes usually works. I did in UK and had results in a couple of hours with a a certificate.
Not sure with the ThaiPass going away whether it can be done on arrival and you bring your own test.