Can I combine my 90-day report and 1-year extension of stay application in Thailand?

You can indeed handle both your 90-day report and 1-year extension of stay application around the same time due to the flexibility offered by Thai immigration. You can file for your one-year extension up to 30 days before the expiration date, and your 90-day report can be submitted as early as 15 days before the due date or within 7 days after.