Is your insurance through your work, or private?
If it's through work, your best bet is to talk to your HR department. You'll need to come out to them anyways, assuming you plan to walk all the way down this path and not just peek around the corner for a second.

They can look into adjusting the coverages of your plan.
If it's private insurance, you'll need to call your insurance company and talk about adding coverage.
All insurance companies should have some appropriation for transgender services now, it's just a matter of making sure it's not carved out of your plan.