Space Engineers has always been comfy for me.
>alone in space (or with friends on a private game)
>mine asteroids, build spaceships and a space station
>explore caves in bigger asteroids
>queue up some comfy music in the background for long sessions
>when you don't want to build, have your ship cruise through the cosmos
Pic related is my terrible mining ship. You can kinda see the wireframes on stuff I still have to build.
Shilling for >>>/esc/ here too, a board dedicated to comfy video games and games good for escaping reality. I'll put a link to this thread in the /esc/ game recommendations thread so you guys get more comfy-friendly traffic.