Hi Smooler,
Others may have different opinions but it it also depends on your personal situation.
I am going to assume that if you are re-locating you have an ongoing relationship with a Thai. For the purposes of this exercise I will assume it is heterosexual and that you are not married.
There is no visa, other than a tourist visa, available to you before you are 50.
The best choice for you would be to get tourist visas until you are 50. Once attaining the age of 50 you can apply for a retirement extension (note here the distinction between a VISA that you can only get outside of Thailand and an EXTENSION which you can only get inside Thailand and runs for 12 months). It will be interesting to see if the new Buriram immigration office (if open!) will convert you from the tourist visa to a retirement extension. NB - have a look on here for information regarding the requirement for a retirement extension - UR LEFT has compiled several 'idiot's guides'.
You may be told to go to Savannaket and get a single entry Non-Immigrant O visa based on retirement - from that you can do an extension. As said, try first when you still have circa 30 days left on your tourist visa.
All the above changes if you are married/get married. You can apply at any time for a marriage extension but should get a visa based on marriage from a Thai embassy first. At Savannaket you also have the option of getting a 12 month Non Immigrant O visa and you just need to do border runs every 90 days.
I will mention the O-A visa at this stage - Google that one to see if it fits your circumstances.