So your stock plug and its upgrade equivalent are OE only - they'll only be available through the dealer for the next few years. If you wanted to get the "official" upgrade plug from the dealer the part number is PLZFR5B13EG but I would take a guess it will likely be somewhere around $25 per plug.
The differences between your stock plug and alternatives that are currently available are minimal. The main difference is the stock plug has the metal shell that extends maybe 2-3mm further. If it makes any noticeable impact we can just close the gap a little bit.