You have a great approach to life! You sound very pragmatic.
I do understand how frustrating and limiting not being able to bend your knee is.
I’m not familiar with Headspace, but the evidence suggests that when performed correctly mindfulness and mediation benefits most people, with the possible exception of people with schizophrenia. If you’re a relaxed person you may find it easier to focus on your breathing or something else, and you may not need an app to help you to learn mediation.
A surgeon who knows about the pathology of arthrofibrosis is likely to refer you to a rheumatologist. Many surgeons will be happy to do more surgery, but in my opinion this is not necessarily the best option, especially while your inflammation is high, because arthrofibrosis is an overly enthusiastic response to a wound, and surgery makes a wound. Your experience with your last surgery will be some guide for you. Did your knee become better or worse after it? Unfortunately, there are no easy answers.