My next perch—a closet my parents expanded to turn into a livable spot for my 11-year-old self desperately seeking my own space—was also furnished with, you guessed it, a twin bed!

Tucked away under a bed, the best trundle beds are a space-saving solution for a kid’s room, home office, or guest room. While the frame dates back around the 1600s, trundle beds are far from ...