Believe it or not, this is quite imprecise.
Since winter is coming, I recommend NON-high mileage 5W30 synthetic from Mobil1, Valvoline, Quaker State, or Pennzoil.
(I won't use Castrol even if I get it for free
If the only symptom is oil pressure which is on the low side of acceptable, you need to measure oil pressure at some other point,
maybe that spot has a partial blockage which is showing locally low oil pressure?
If your radiator has a motor oil heat exchanger, oil pressure will go up slightly once you bypass it.
So long as you keep using synthetic this should not be an issue even if your engine works or plays hard.