It's pretty much a crap shoot what you will get as replacement foam. I did a set of '60s Mustang buckets, and the new foam was so firm it wouldn't let the seat back sit upright. I've gotten other foam that was so soft it was almost non-existent.
Those two places probably have the same supplier, so go with the less expensive ones. If they show up and they're too soft, return them and try the other more expensive ones to see if they're better.
The only other alternative is to have new seat foam custom made by an upholstery shop, but that's going to be pricey unless the seats are very basic.
No one lives forever, the trick is creating something that will.