O2 Sensor preventative replacement

Hello,

I would like to replace the oxygen sensors as preventative maintenance. No Check Engine Light.
I purchased the car from a guy in California and I believe this car has 2 O2 sensors and 2 Air Fuel Sensors following California emissions requirements.

How can this be confirmed?
Should I get these OEM or from places like AutoZone/O’Rielly/Amazon?
I have seen them much cheaper on Amazon using part numbers from Toyota Parts OEM.

However, I have heard you need to buy California Approved emissions O2 sensors if it’s made in California, but I live in Minnesota where there is no emissions test.
However, I would still like the vehicle to run as optimally as possible even if it means buying California O2 or A/F sensors.
Not quite sure how to go about this.