I have pulmonary fibrosis, on continuous oxygen and have had both regular PT and Pulmonary Rehab. Your husband's oxygen needs are a priority with any activity or exercise. And as hard as it seems, activity is what will help him increase his stamina and move forward with his recovery.
If you aren't familiar with Pulmonary Rehab, it's a supervised exercise program that includes cardiovascular exercise (treadmill or NuStep/seated elliptical type machines) and light free weights. The programs are customized for the patient's abilities. The therapists keep track of oxygen needs, heart rate and blood pressure. They have oxygen tanks there that patients can use while doing their programs. It might be worth asking his doctor if something like that would be beneficial. If he goes to PT, they should be set up to deal with oxygen needs.