There should be two oxygen sensors, one above and one below the first catalyst. Usually the top sensor fails first, but I replace them in pairs.
If yours are the original sensors with almost 200k miles on them, I would not spend money to pay someone to tell me that they are getting old (which they are by now), and then pay him over $100 each for new sensors. I would buy a new ones on line and put them in myself. It will cost you about $80 each for sensors that fit or $40 each for generic fit that you have to attach your old plug to.
You have literally nothing to loose by trying new oxygen sensors, because if you do need a new catalyst, you will replace the sensors as well.
I am not certain, but I presume that the two catalysts are completely different. One promotes reduction (removal of oxygen) of NOx, and the other promotes oxydation (addition of oxygen) to CO and VOC.
You can’t relocate the downstream the oxygen sensor, and even if you could, doing so would cost more and be more work than replacing the sensor.
People often scold me for “throwing parts at the problem” but if I have to remove a part to examine or test it, and it is a part that is subject to failure and it has over 100k miles on it, there is no point in testing it because I am not putting that old part back on my car.