Interesting that the seller is in Houston - so are these guys that I found on eBay. Might be the same seller, might not be.
https://www.usautoseatcover.com/
I got a seat bottom for my '06 SS from them. I also made the same mistake and assumed the foam was OK when in fact it needs replacing. It's OK as I made a little error here and there on my install (first time around doing one of these) so I'll end up going back in at some point and replacing the foam and the heater element. The quality and fit of the cover seems pretty damn good.
You can tell the difference but to me that's expected with new vs. old, the new stuff won't have the wear/tear and crud build-up on it. There's tips around the 'net on freshening up your old leather to match - I wanna say Seat Shop videos talk about it, IIRC.
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Richard