I did a similar study many years ago then actually moved to the city. It was wonderful, the climate was perfect for me. Moderate all year, low humidity, low wind and rain.
Guanajuato, Guanajuato, Mexico was the answer for me. I will move back there when the kids are older.
Basically quite a few places in Mexico. La Ciudad de México or Ensenada for me. I intensely love Mexico City but Ensenada is where I'm moving to. Entirely for health insurance reasons. I will be there tomorrow hooray.
There's Guanajauto, but also Querétaro, San Mig, León. The central highlands are big and agreeable.
People here love San Diego... I know San Diego really well, and I think Ensenada beats it in every way. San Diego is like a little brother to LA. It sure seems like it would be great to live there, and I suppose if you are desperate to spend quality time sitting in your car crawling in traffic it is ideal, but that's not for me.
Proximity to the US border. Medicare, particularly. I am no expert even though I have spent a lot of time on it. It seems a double cancer survivor with partner much the same is going to have a hard time getting insured any other way.
Guanajuato, Guanajuato, Mexico was the answer for me. I will move back there when the kids are older.