Hey Kate,
I feel for you. For an active person that length of recovery time does feel like a death sentence.
I'm a 50 years old, and I've had about eight surgeries in the last 20 years (I've lost track!), all for muskuloskeletal injuries, all with recovery times like yours or longer. Like you, I am addicted to exercise, and have been since I was about 14. Also, I have ADHD and OCD, which are partially releived by exercise. And I have a family and a child. Which is to say, if I can get through it, you can get through it!
I have come to see the surgeries and the down time as a "time out" from life. Nobody can demand anything from you, and you don't have to feel guilty about just resting. I would just embrace that--it's not often in our crazy lives that we get a real chance to slow down and rest.
Then, when you are ready, you could try new light exercises. Running or walking with a foam floation belt in a swimming pool is really good. Some physical therapy centers of gyms have "hand bike ergometers" (don't laugh, we do what we can!). Static balance poses can be really hard (stand on one foot with your eyes closed...now do it with you torso inclined and one leg extended backward). Light ski ergometers or ellipitcals or whatever other machines for cardio could work. Maybe you're worried about finger strength? Get some grip trainers or use a bucket of rice and develop the most iron grip ever.
Just don't overdo it. I think you are absolutely right to focus on the internal wounds rather than the external incision. You wouldn't want the internal wounds to start bleeding. And that does make your situation difficult, because you don't want to excessively move your torso and abdomen, or put any stress or tension through your core. It's going to be hard.
But you have no choice, right? I've heard endometriosis is really painfull, as well as underdiagnosed. So this is a positive step. Hopefully in the long term you will have less pain.
So accept. Adapt. Go slow. Be creative. Try to see it as an opportunity or turning point. You will come back stronger.
Good luck, and hang in there.