A std oil pressure gage and a cheap one is just fine. Just like the fuel pressure gages only for higher pressure. You can mount a tee at the "sender port" or the aft port near the oil pressure adjustment.
I had both an electric on the gage panel and a mechanical one mounted on the engine so I could see it with the cover off. I cold started my engine with the cover off using a permanent remote start switch so I could see both fuel and oil readings.
Dave Neptune