You could replace the factory switch with an aftermarket sensor for a gauge, but you would have a constant oil pressure warning if you didn't terminate the factory wires.
You could install a T fitting, keep the factory switch and add the aftermarket gauge/sending unit.
You could replace the factory 7 psi switch with a 20 psi switch so you would know sooner if you had an issue.
You could add a gauge and sending unit on the oil gallery port on rear of the head.
Pros and cons to all of these options, be it cost, complexity, reliability, or ease of installation.