Renault laguna 03 1.8 o2 sensor or coil??

Hi guys, i have just had my mot done on the car. They popped it on the diagnostic and the engine(orange) light went out and they said it does say the second 02 sensor had a fault but its cleared itself. Now after driving it for around an hour the light has come back on. After reading around i see alot of people saying that this also could be the ignition coil. The garage has quoted me £174 for the sensor and fitting which is kinda alot. The car itself runs okay, ive noticed at times it idles a little low or a little inconsistent but it isnt that bad at all? Am i right in thinking this can damage the cat converter etc if i dont get it done? any opinions on this please?



thanks