Typically, insurance companies require a letter from a mental health specialist, a doctor monitoring HRT (1 year), and a letter from your surgeon (here's a template.)

I'm not certain if Medicare and WA Medicaid have similar requirements, but I imagine they do. If you can't find this specified in the "fine print" of your coverage, it's probably best that you seek to satisfy the requirements somehow, because if your claim is denied you could find yourself on the hook for the surgery fees.