I have asked some airlines and they pointed me to Thai consular site. It does say that if you have a proof of recovery letter then you do not need a negative PCR test to fly to Thailand. It does not say that once you land in Thailand whether you still have to take that PCR test on day one and day 5.
I am planning to fly to BKK and then stay one night there and then fly to Krabi, stay there 2 nights, then go to Phi Phi for one and night and then move to Phuket for the 2 nights. Then fly back to BKK from Phuket.