If you can spare a few hundred dollars, a good Thai visa agency can simplify and de-stress the retirement visa process. Google for visa agencies in your area. Find ones with +4 star reviews. Visit one or two, to compare their prices and how well they communicate. There's no charge to talk with them. They made my retirement visa much easier than expected. Their fee was worth it.

Under ideal circumstances a METV can last almost 6 months.

Near the end of your first 60 days, extend the visa at an immigration office, which adds 30 more days (for a total of 90 days). At the end of those 90 days, leave Thailand briefly. When you return, the immigration officer will give you another 60 days. Near the end of that 60 days, go to immigration and get a 30 day extension. That's a total of 180 days.

The only problem I found is that, the METV visa has a 6 month Maximum expiration date. Immigration won't give an extension if it finishes after the Maximum expiration date.

Keep in mind, the main purpose of the METV is make it easy for tourists to go in and out of Thailand while on a several month trip to SE Asia. Although it can be used to stay for almost 6 months, that's not why Thailand offers it.

Also, AFAIK Thailand will not issue more than one METV to a foreigner in a 1 year period.

If you want to stay longer, get an education, retirement, or Elite visa.

IMO, the VIP visa service agencies are worth the price. Google the visa agencies in your area. Look for ones with 4 or 5 stars. Then look for reviews of them on Youtube. Then visit their shop to see if they are professional and communicate well.