Greetings Simon,
Thank you for sharing your situation.
I have been following this thread since your first post and generally noting the comments/advice/recommendations of others.
I have a farang friend here, in his late fifties and recently diagnosed with Stage 3 cancer. He has an ex-wife, children and grandchildren "back home", as well as a Thai wife and young family here. He is also struggling with deciding whether to stay here or go "back home".
Myself - I am nearly 70, in slowly declining physical and mental health; no family here and no family "back home".
One issue which has not be addressed (unless I missed it, if so my apologies) is who will take care of you as the end gradually approaches (when you have mobility issues, unable to dress yourself, unable to wash or go to the toilet by yourself, your need assistance in eating, you are bed ridden, and when you need constant medical attention). Having had several friends "back home" progress through these phases, I have had some experience with this concern. Apart from the issues already discussed (financial, accommodation, etc.), I think the above issues are important and you could privately address them with respect to staying in Thailand, or returning "back home".
It is a matter of "horses for courses", as they say - we are all getting old, but our personal situations - health, family, financial, access to health and palliative care, etc. - vary from person to person.
A final issue, which many do not "discuss", is a controversial one, and that is access that to what some in the medical field call MAiD - Medically Assisted Dying, or euthanasia. A question for you to answer privately - if the pain gets too much, and medications do not help, what do you want in these final days? A dear close friend died "back home" in early 1994; he was hospitalised with end-stage cancer, was in agony and the medications he was given did not reduce the pain level; in the end, he begged his wife (a retired health care professional) to end his life; which she did with an overdoes of opioids (for memory); she was thankful that he died peacefully, and not in agony.
Good luck with your decision-making.
And thank you for sharing.
My sincere apologies if this reply is too long or too distressing.
Sincere best wishes.