I found House of Body Narat to be very thorough and good.
https://maps.app.goo.gl/Uw4pE9vsSmW6gC7cA?g_st=ic
He’s in Soi Nantaram, on RHS, driving away from Rat Chiang Saen Rd, which is the road outside the moat, on the southern edge of the old city.
I paid for a Professional RAT test in Oz at my departure airport within 72 hours before planned arrival date in Thailand. Q-tips were inserted up each nostril, but not far up. Waited one hour. The Cert was 3 pages long, including a QR code and details of certifying company - one's passport details must be correct. I downloaded the Cert from email onto my phone. Required by airline at Oz check-in, then Cert was photographed with passport by Thai Health Officer before being allowed to queue for entry Immigration stamp.