Vinyl Seat Conditioning

[ls6owner]

I am looking for some recommendations on how to best clean/preserve vinyl upholstery. I am working on the original vinyl interior on a 70 Chevelle. To clean, I have used a mild soap (Simple Green) and water, which worked quite well but wonder if others have any suggestions that are better. My bigger concern is how best to treat the seats to keep them soft so they don't start cracking and pulling apart at the seams. Thx in advance for your assistance.
Oliver