ถนอมศรี **********************
@Tony ********
if you have the economics in place you actually only need a single entry Non O. Travel down to Thailand apply for the extension of stay when you have about 30 days left of your stay.
If the application is approved you will have new stamps in your passport with the permission to stay. This is when you can buy the reentry,
If you plan to make a borderbounce before you apply, ie if you want to stay more than 90 days before applying, you need the multiple.
Depends on how you plan this.