Try this...
An artifact in a nebula maintains a volume of breathable air. How this superscience works the survivors of a long lost spaceship can't answer. The volume is vast, but solid matter isn't that common. Soil to grow crops in is rare. The tree reefs ( genetically engineered organisms that provide shelter and food for the stranded survivors) are carefully nutured as the basis of survival.
This is a TL3 society with a scattering of ancient TL12 items, some of which are supertech. The surving humans are all descended from transhumans bred to survive microgravity and still be able to function in One G or more.
Yes, I'm stealing from
Intregral Trees but I never read the book.