I do not understand the leap from saying that health has much more to do with 'environment' than mainstream medicine yet tends to recognize, to saying that the relevant 'environment' here is a kind of psychological environment. In fact you go further than that, to describe the relevant environment here as a kind of psychological precursor ... a sort of fundamental outlook or frame of being which is itself a kind of antecedent even to psychology. I don't get how you get there from what you said about environment and homeostasis. Couldn't the relevant 'environment' be an environment of inflammation or nutritional imbalance or rampant yeast or a dearth of dopamine etc. I suppose you'll say that all of these too would be downstream of some fundamental psychological environment. But I'm not seeing how you get to that conclusion with such certainty.
Forgive if I'm misunderstanding you. I'm sure I am. But to say that to get better from chronic pain or anxiety or depression, "you have to change who you are as person, for a majority of the day" strikes me as implausible. Is this any different from the "push through it," "stiff upper lip" modality which was so prevalent for so many decades and, I think, added to the suffering of so many? Aren't outlooks and thoughts themselves subject to the influence of environment and brain chemistry and disease? Isn't this one of the epiphanies of mindfulness meditation: that we are not the author of our thoughts? I don't view thoughts as some neutral territory where we can just choose to think what we like and then over time reap the benefits of choosing better thoughts. CBT for example is a kind of indirect way of affecting our thought patterns over the long term. But it's nowhere near as simple as saying 'be a different person until I feel like a person who is better.' I do not believe that we have it in our gift to make ourselves anew everyday like you say. I think we are very much subject to the constraints and of our body and environment. Can we affect who we are with intention over time? I guess, to an extent. But if you're telling me that the way for me to get out of chronic pain and depression is to start being today, this minute, every minute, a person who is not in chronic pain and depression ... then I don't really know what you're saying.