What legal options do I have for a long-term stay in Thailand without a work permit or marriage?

Great group! Thanks for the add. Been scouring old posts and comments for a few hours but thought I'd get some more specific answers. I'm 46, and a US citizen, currently I'm on a 1 year extension of my ED Visa (feel free to correct me on terminology). I was attending an international university in Bangkok, but now that my semester is over I don't think I'll be going backs. My extension is valid till May of 2020, but it's likely that if I don't register for any classes by the end of the late registration window at the end of July I'll be disenrolled and the school will report it to immigration at some point. I've never had a problem with immigration in the 11 years I've been coming here and I don't want to start now. What are my legal options for a non-working, non-married, non-business owner, long-term stay? I've explored doing the "language" school option but seems like some folks still have issues with this on occasion. I've also explored the Elite visa option, but technically I only need it for 4 out of the 5 years before I can apply for a "retirement" visa/extension. Am I missing an option that I didn't read about? Thanks in advance for any insight.