So, I haven't had my surgery yet, and don't have any personal experience to really add to that end of the discussion, but it does sound like you're freaking yourself out a bit. Anxiety is to be expected, I think, with any massive life change.
From what I've read in these forums, and seen in the videos I watched of people who have undergone the surgery, the main culprit for splits tends to be the partner not being supportive (for various reasons like insecurity, jealousy, control loss, ect.), or the relationship had underlying issues that were made worse/more apparent by the lifestyle changes and new found confidence. Based on what you've written, neither of those would apply to your relationship. You sound like you're doing as much as you can to support your wife, and that's honestly really amazing. Be more kind to yourself
If you are finding that you really can't shake the anxiety, it may be beneficial to see a therapist too. I'm a huge advocate for therapy for basically all things mental health related. The surgery is definitely a big change, and a neutral third party who is trained in such things can help you navigate the feelings that come with it.