May I suggest that you hand it to a competent mechanic, not a Nissan main dealer, to test the two oxy sensors heaters & two control circuit/connections to determine which of the two O2 sensors, front or rear, is suspect & to order & fit any parts required.
With ignition switched off, sometimes simply unplugging the O2 sensor & cleaning the connections, can clear a fault code after a few stop start normal running operation cycles.
If determined with a DIY solution & having determined whether you need a front or rear O2 sensor, call the local auto factors trade parts suppliers with your vehicles registration number & they can identify what’s required without any part numbers.
Be sure to ask for trade prices for your employers business name from three separate auto factor sources.
References: K13 Micra diagnostics code P0031 at DuckDuckGo
K13 Micra Oxygen Sensor Prices at DuckDuckGo
Good luck & let us know how you get on?