Actually you could try to rejuvenate the old O2 sensor if you want to add a bit more miles to it. Get the old sensor out, wipe out any carbon deposits on its tip and heat the tip (until red-hot) at a gas cooker/burner. Hold the sensor body using some long-handle pliers as it could get really hot with your hands near the flame.

If you could connect a digital voltmeter (set to very low voltage reading) to the sensor while doing the above you could see the voltage fluctuating up and down (0.100 to 0.800 mV). The sensor may respond sluggishly at first. Keep heating it for about 5 minutes or longer before it starts to respond. Consistent low voltage reading (less than 0.100mV) means the sensor is already out/kaput.

And clear the OBD codes after installing the rejuvenated sensor. Either disconnect the negative battery cable (but this may need you to enter the radio codes again) or press the ODB button longer than 8 seconds, the LED stays lights up, then press for longer than 8 seconds again until the LED turn off. Check back immediately if the codes are cleared by briefly pressing the button and you get a 1-1-1 code.

Bosch three-wire O2 sensor recommended replacement interval is between 60k to 100k miles. For Regina (NTK sensor from NGK) about 150k miles.

Done this many times.

May this helps,
Amarin.