My friends and I were big Retief fans in college. It seemed that everyone who liked Retief also like The Stainless Steel Rat series.
https://en.wikipedia.org/wiki/The_Stainless_Steel_Rat You might want to look into that as well. They make nice companions. Retief is written more for adults but are accessible to younger audiences while The Stainless Steel Rat series is lighter and can be enjoyed by younger audiences as well as adults.