The Sims get sick even going outside because the air quality is so poor. They moved into the off-the-grid shipping crate home in Port Promise, which is an industrial port area in a terrible state, and promptly became abjectly miserable. I made a pair of Sim eco warrior roomies called Britta Horace and Nigel Sneed, along with Britta's small and lazy mongrel dog Graham.
I'm trying out various different new things in the new neighbourhoods added with Evergreen Harbour, but so far I can say that living in an eco-friendly way is hard, especially if you're off the grid.
I am working on my review for The Sims 4's newest expansion pack, Eco Lifestyle, in which you can choose to live carbon neutral or carbon positive, but so far, it is fun.