Keep the box
Put a plain cardboard box somewhere mildly inconvenient. Add crumpled paper. Congratulations: architecture.
A nicer home, according to cats.
No luxury pet furniture required. Cats mostly want choice, predictable calm, and the box the furniture arrived in.
Offer a lookout
Clear a stable window perch or high shelf. Height lets a cat observe without participating—a premium feline service.
Rotate toys
Hide half the toys for a week, then swap them. Novelty returns, the floor gets cleaner, capitalism briefly loses.
Make a quiet zone
A bed, chair, or carrier in a low-traffic corner gives the cat a place where nobody reaches in uninvited.
Leave a sun patch
Notice where sunlight lands during the day. Move a cushion there and let thermodynamics do the rest.
Add texture
Provide sturdy scratch surfaces in both vertical and horizontal orientations. Put them where the cat already scratches.