What are my best options for extending my stay in Thailand for six more months after multiple visa extensions?

Enter on TV for 2 months, extend one. Border bounce, visa exempt 30

Days extend 30. That’s 150 days. Fly out. Obtain new tourist visa and repeat same same process for another 150. If you decide you need more time, consider long term visa options.

For 6 months you can just stick with border runs and extensions as long as you use a border run company. Border runs are limited to 2 per annum, so 1 before the end of this year and you'll have 2 starting in January. I wouldn't be tempted to try it on your own though.

The best plan would have been to get a multiple entry tourist visa from the US before coming to Thailand. With that you could get about 9 months total.

Now your best bet is probably to go to Savannakhet (no appointment needed) or Vientiane (appointment required) and apply for a tourist visa. Then return and do the 60+30 days and then use a border bounce agency to get another 30 day visa exempt + extension, and do this 2 times. Then you'll get your 6 months and shouldn't have any issues since you'll be using an agency for your entries.