I also think your personality will be a huge factor in what type of job would be stressful or not. I'm a somewhat shy and very introverted person who gets stressed by talking to and dealing with people. So some of the jobs mentioned above would cause me deep stress. Solo dog walker or working outdoors in a wholesale plant nursey or on a physical project like building something with people who aren't chatty would be a better fit for me. So make sure you look for things you enjoy that don't increase your personal stress levels.
This is exactly my point above. For a low stress job, it has to be easy. Whether a job is easy or not entirely depends on the abilities of the person doing the job.
I had a part time ob early in my grad school program that was stupidly easy for me. I was moderating virtual condo corporation meetings. This job was stupidly easy for me because I had been a condo corporation president.
It paid $30-something per hour, and was the easiest job I've ever done. But some of my coworkers really struggled with it because they didn't know the inner workings of condo boards, and couldn't anticipate when fights would break out, so it seriously stressed them out.
Anyone who has worked entry-level jobs can probably remember that they're often the furthest thing from 'low stress" for a lot of those employees. What makes a job low stress or high stress is how challenging it is and how high the stakes are.
Dog walking would be easy for someone who is really good with dogs, but walking a pack of dogs could also be an insanely stressful task for someone who doesn't know how to break up a dog fight. Hell, managing one decent sized dog can be extremely stressful for an inexperienced person if that dog is reactive.
For me personally, my most favourite "easy" job was working as a children's science entertainer. Which was only easy for me because I'm really good with managing groups of kids, and I'm a confident performer. Another person could find that job horrifyingly stressful.
It all comes down to what the individual finds stressful.