.Hi rmfields, take it easy to start with is my first advice.
About 8 months ago I was diagnosed with severe COPD but took to the gym and now my results indicate mild COPD! I started off at the gym 1 to 2 mins on the rowing machine, cross trainer and bike. I live in a hilly area so walking is not so easy. I feel I built my fitness up by little and often steps - increments of 15 seconds. I don't touch the weights I just try to do a little more each time and build up my endurance. Sitting in the chair on bad days lifting bottled water in each hand maybe 5 times maybe 10 whatever I can do comfortably. Leg lifts whilst sitting - just building up each time.
And of course don't give up, keep it going even a small amout is better than none. I kept a diary of what I was doing 1 minute built up to 2,3, etch now 15 mins is okay but take it slowly you can always repeat the exercise again later rather than doing too much in one go.
I hope this helps - keep going