P0430 after misfire bad coil

Hello: first timer here. I had a bad coil in cylinder 6 misfire. Drove it only a short (1/2) mile back home. Check engine light came on with P0430 code. I replaced coil and spark plugs. Light never went off. Used a bottle of cat cleaner and it still stayed on. Replaced downstream O2 sensor and that seemed to do the trick. However, about a month of driving it it came back on again. I haven’t taken it to a mechanic and my skill set is probably not sophisticated enough to replace CAT. Should I replace upstream O2 sensor and see if that works? I’m concerned it is the CAT but I don’t want to spend that kind of money on this vehicle that has 215k miles. Any help would be appreciated. Thank you!!

 

Fuel injector was my misfire problem not the coil pack.