I will second Gil's recommendations, but if you want to DIY then small pressure gauges in the 30 PSI range are available from multiple sources, like ebay:
https://www.ebay.com/itm/115385897140?However, the problem being that you will need to make an adaptor to fit the Jensen threads!
I will add that you really don't NEED a pressure gauge, as your Safety Valve will actually be all the pressure indicator you really need, but I will also add that having a pressure gauge is sort of fun and does add another dimension to steaming up!!!