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I'd HIGHLY recommend getting Nitrox certified, and I can recommend some instructors, if you like. I don't understand your comment about needing a gauge -- You either need a computer that does Nitrox, or Nitrox tables, but they aren't complicated. The shops where I have bought Nitrox have all had analyzers and a log of tanks picked up and their mixes.
Whether you believe Nitrox helps with fatigue (I do), or that older folks are more susceptible to DCS (I think we are), or you want to extend your bottom times and/or reduce the risk of DCS, Nitrox makes sense. If nothing else, the course is interesting.