"Clogged up cats" are not what they used to be. In days of yor when leaded fuel was still available it was possible to clog a pellet-type converter with lead. Now, not so much. If the converter is clogged it's because something has physically blocked the converter matrix (debris, and not likely unless the engine is coming apart internally) or the ceramix matrix has collapsed (what happens when it gets too hot and begins to crumble).
If your converter is truly clogged then there's no Super Potion Juice on the planet that will fix it. It'll take less time to replace the sensor than to go fill up with gas and "Wonder Juice" (or should if it's a downstream sensor). Go ahead and buy all of them. You need them anyway given your mileage.
Be sure to unhook the battery while changing the sensors. That should clear any problem codes and force the computer to do a new learning cycle with the new sensors in place.
Brad