#2 – The Feel
Your sofa is either going to feel plush and soft or hard and dense. Polyurethane foam comes in both soft and denser cushions, but the hard cushions seem to last longer while the softer cushions tend to deteriorate quickly.
If looking for alternatives in cushioning, the polyester fibres are inexpensive but are not as resilient, and goose down cushioning is heavenly, but it also clumps in places.
Test the springs to see if the sofa provides enough support. If possible, a good way to check whether the springs are good is to feel them, and if they are close together, they are more than likely going to last.