The seat isn't going to have anything like that. It will have a switch to add or subtract air pressure that is supplied from the on-board air system of the truck. What you're attempting is custom.
With you having a little 12v compressor, I'd suggest putting the compressor on a toggle switch(add a relay if needed), switch the compressor on, air up the seat to your desired height, shut off the compressor and seat switch, and then see how long it holds.
You can add a check valve at the outlet of the compressor, but I'm not sure if you would necessarily need one, the seat switch should handle that.