What is the most efficient way to invert digital signal? NPN, MOSFET, logic gate
A 900 nA static current is ok for your application?
https://assets.nexperia.com/documents/data-sheet/74AUP2G14.pdf
This one has a higher worst case (2uA, 100nA typical), but you would need only one IC:
https://www.ti.com/lit/ds/symlink/sn74hcs14.pdf