The secret to an epic fort is structure.
Use couch cushions as walls, not roofs (they’re too heavy and will collapse). Drape blankets over chairs, tables, or brooms propped between furniture.
Clothespins or chip clips hold blankets together at corners. Weight down blanket edges with books. Add a flashlight, pillows, and snacks inside.
For outdoor forts, lean long branches against a tree trunk in a circle, then weave smaller branches through them horizontally.