I also suffer breathing problems. Small dogs like Yorkies and chihuahuas really don't need exercise like big dogs. They get enough running after us in the house. Consider their legs... they have to walk 10 paces to our one step (unless it's a Yorkie over 10 lbs). They do require fresh air so letting them in the yard to run is good. My Muffin plays fetch and will chase a ball for about 5 min before she tires out. Inside or out is considered enough exercise for our little ones so don't worry about it. If you want to hire a dog walker, then do so but don't cause yourself undo stress because they pick up on that in us and then they get stressed.
Just have fun and don't worry.
