Hi @Poppo, and welcome to the forum!
I saw your message to @Luke describing your struggle to play single notes cleanly. While I personally am more of a single note player, I really enjoy listening to the music made by those who have mastered the various techniques of multiple note playing!
Now to your issue: COPD and the associated breathing problems. Better than me writing a detailed, long reply here is for you to visit the Seydel harmonica company’s online site – and in particular this page about their Pulmonica harmonica. It is not cheap (priced around $150 with harp and instruction book in English) but the medical test results are quite impressive:
- Better breathing in as little as two weeks.
- Better clearing of secretions with only 5 min. use twice each day.
- 13% improved quality of life after 8 weeks of use.
- Exhalation pressure (FEV1) improved 34% after 8 weeks of use.
- Vital capacity (FVC) improved 46% after 8 weeks of use.
So it is definitely worth checking out!! 
Another page on the Seydel online site about the Pulmonica is this page.
If you and your doctor decide to give this a try, but you prefer sticking with the regular diatonic blues harp and following the lessons that @Luke provides, then I would suggest moving to a lower tuned diatonic harp (such as a Low D or Low C harp – the Low C would be the same as used in most of the lessons from @Luke but is just one octave lower in tone), and Seydel has a great selection of low-tuned harps ranging all the way down to a Low-Low E 
The reason for lower tuned harps is that lower frequencies (tones) played as chords (more than one hole at a time) are better at loosening the secretions in your pulmonary system.

The models in the 1847 Classic Low line-up include that Low-Low E model (priced around $90), while the less expensive Session Steel Standard Richter line-up “only” go down to Low C (priced around $60). If you can afford it, I would go for the 1847 models. 
Be sure to first consult with your physician and tell him/her that the research concerning the Pulmonica was done by Dr. William Weiss at the Senior Friendship Center in Sarasota, Florida. Here is a collection of videos about the Pulmonica.
What I almost forgot to say about the Seydel harp models that are mentioned above: they all come with stainless steel reeds (which last much longer than the usual brass reeds found in almost all other harmonicas). 
More questions? Just ask! 
Best regards,
– Slim