Like you I have Hypertrophic Cardio Myopathy which kicked off my AF in September 2015. After 6 weeks of real breathlessness and being unable to walk I had the Electro cardioversion procedure. It was slick and painless but I didn't get an instant result. It took at least 3 days until the heart slowly recovered.
Now, 6 months latter, I'm on anti coagulants (aren't we all) and 5mg bisoprolol. I was never thin but I have moved up one trouser size since the AF attack. I'm back at work but still get very tired and breathless on mild exertion. Maybe this is my age (57).
I would be interested to know what's been suggested for you as I think the added complication of HCM makes putting a "fix" in place more of a challenge .