I am racking my brains trying to think of a job with the description you wrote. The first thought that came to my mind was, working as a parks employee? Cleaning the park, mowing grass, pulling weeds, etc. It's a focused job, not too much multi-tasking, you're working with nature and less with people. Nature has a way of calming us down, apparently. 20 minutes a day outside does wonders.

A good friend of mine wanted to go into horticulture. She and I have similar traits, both introverted, enjoy nature, and less multi-tasking in a stressful environment.