The gap between a $1,500 sofa and a $4,000 one comes down to five specifications, and one of them predicts more than the other four together. Seat foam at 1.5 pounds per cubic foot flattens in two to five years.…

A standard 32-inch interior door gives you about 30 inches of clear opening once the slab and the stop are in the way. A typical three-seat sofa needs 33. That gap of three inches is the reason sofas end up…