Here are some guidelines about the cultural setting.
* Space-faring culture which dominantly lives on ships and stations, with artificial gravity, but is in some ways quite medieval; they don't *make* anything, but rather, are traders who rely upon other cultures for industry and production.
* Physicians are called "Healers" and the job incorporates aspects of religion and spirituality. Healers help the body heal itself. Some techniques are quite high-tech (stasis) while some are remarkably low-tech (appendicitis is still a leading cause of death). Strangely, they're quite adept at healing cancer, while other things (particularly if it's tissue that doesn't naturally regenerate, like the lungs) are a death sentence. They don't believe in prolonging life at the expense of quality of life.
* Culture-wide, they don't believe in cutting into the body (see bit above about appendicitis), not even a Caesarian section to save the life of a mother and baby
* They don't have a problem with drugs/herbs/hormones to treat conditions.
* Culture-wide, a person's wish to die is always respected; this is sacrosanct. Only a person can make this decision for themselves.
* The culture generally sees death as the result of life. Most religion revolves around ancestral veneration. All people who make a contribution are ultimately remembered. They don't think much about an "afterlife". Your afterlife is that you'll be around in some form, preserved in memory by your descendants, and you'll be able to guide them.
* Most people don't like to admit that they're sick, and would sooner die than be dependent upon technology or have to lug around big heavy symbols of impending doom.
* Most people die at home.
* Your family is likely to get annoyed with you if you insist on sticking around and dragging things out, just for the sake of staying alive. Staying alive isn't a good enough reason in and of itself, to stay alive. There is a strong cultural pressure to remove one's self from existence if they stop being productive in some form. My character would still be considered productive - he's a spiritual leader, and probably can continue to do some of his work (such as writing) fairly late into his illness.
I'm just trying to get an idea what my character's life is going to be like in his last few years. What might they have, technology-wise, other than the ubiquitous oxygen therapy? A silly thought, but might there really be something like "tri-ox compound" like in Star Trek?
It occurs to me that in a culture that doesn't practice much in the way of artificial life prolongation, it might be more likely he'll die of a complication (such as pneumonia or heart failure) than the end stage of the disease itself, so he may only have moderate symptoms at the time things really go downhill. It might be similar to a person in a lower-tech culture who developed emphysema. How long would it take a person to die, in that case?
A final point: COPD is a rare illness in this culture, given that most people don't engage in the lifestyles that predispose people to the disease. Somebody who got it *would* have my character's history (history of lung injuries and repeated infections). Certainly a healer would diagnose it, and be able to offer what treatment was available, but it doesn't exist very much in the common consciousness; it's not what you expect someone to die from. Many people of average education have probably not heard of the illness.
Accidents, strokes, heart attacks, pregnancy complications, and appendicitis are among the most common deaths, so most deaths are likely to be fairly sudden. The idea of a person dying of a long, drawn out disease probably isn't much in the common consciousness.