I am told by immigration it's a straight forward process with the usual photo copies of passport, photos etc. Our immigration office has known me a long time though. But am sure the process will be the same as before minus the need for the embassy letter
neither a Non O for retirement nor Thailand Elite require health insurance. Although I have had insurance for the past 6 years. I got TE to take me to retirement age.
if you are switching from one type of visa to another you have to leave in most circumstances unless you're on a tourist visa in order to convert. They won't do it inside the country.