I've been living in the PI with my significant other, but it's getting long in the tooth so-to-speak (the country). Considering getting  a retirement visa and relocate to Thailand, but would want to have my girlfriend to join me with as little hassles/complications s possible. I'm guessing getting married and having her as a  spouse would be the most straightforward, but besides that, what options exist? 

I'm sure I'm not the first to want to do this/plenty others have come before! Love to her related feedback and experiences. thanks! 

If married it would be no problem for her to get an extension as your dependent after you get your extension of stay based upon retirement.

There are not many other options. Tourist visas, finding work and getting a visa and then an extension or going to school.