You can't really diagnose which parts you need just from engine codes...these codes are hints, beginning markers, to various systems an circuits. The computer does not tell you what part to replace only what parts to test.
Having said that, reduced engine power means the engine is protecting itself or some other component.
If you have a bad 02 sensor, this could throw off the fuel/air mixture, and damage the catalytic converter.
So I'd have the 02 sensors TESTED by a competent shop