That cheap, UV damaged, uncomfortable cushion may catastrophically fail. The size of the parachute is another factor that affects many pilots. Unfortunately, the strongest, safest parachute for some, probably will not be the smallest. Comfort and size may have to be sacrificed somewhat in order to enhance your chances of survival in an emergency. Before you purchase a parachute, whether it's brand new or used, please find a parachute rigger that you trust to help you make this important decision.
Education is the key to making an intelligent purchasing decision.
I don't expect you to know everything about parachutes. That's my job. Only then did you consider spending your hard-earned money. Call me or talk to your rigger, but communicate with someone who is knowledgeable about emergency parachutes. Ask questions until you are satisfied.