The answer is simple, I have aftermarket Recaro seats. They’re also heated by the way. It’s odd they would remove a feature that comes standard on Recaro seats.
Both the driver and passenger seats have the OEM bottoms, only the seat back is Recaro. Compare them to true Recaro bottoms and the bolstering doesn't even come close.
The company I sourced them from is named in the picture of my replacement seats. The Recaro Sporster CS will come with exactly the same side airbags the Z Nismo uses but you will have to transfer the passenger airbag sensor from the factory seat over to the Recaro.
I performed this exact mod on my 370Z Nismo, transplanted Juke Nismo Recaro seats into them (you can kind of see them through the windshield in the picture below) and will attest that it’s a lot more involved than just going the full aftermarket route. The Juke has a taller, more upright seating...