Perhaps consider the METV (Multiple Entry Tourist Visa). It's perfect for stays for up to 180 days with unlimited exit/reentry and no interactions with immigration. You are required to exit prior to each 60 day stay to extend the visa for it's duration. I don't know your status but as an American you might find it prudent to consider being in the US for part of the year to use your Medicare coverage. You'll also find it easier and less costly to purchase travel insurance to cover you for the time you're in Thailand.
According to the Australian Institute of Health and Welfare: "When comparing the proportion of obese men and women across OECD countries, Australia had the 2nd highest proportion of obese men (32%), behind the United States (38%)." Don't worry, you'll catch up.