Typically P0420 is due to a bad cat, and not a bad o2 sensor. That code actually says the o2 sensors are working, in that they detected the efficiency of the cat is below the established threshold.
As for the code you now have, P2238, based on what you've done, I would lean towards the first o2 not being plugged in, or a broken wire. Basically, that code says the first sensor has no reading.
https://www.engine-codes.com/p2238_toyota.html
You can pick up a cheap bluetooth code reader on amazon/ebay. $10 for the reader, and $5 for the TorquePro app, and you can actually read darn near any sensor the car has and verify the live data.