Match cushion circa 1990

[Ingarden]

We recently bought a vintage sofa online that is a match to one we've had for almost 30 years.  Cosmetically they both look perfect and identical (though in different fabrics), but the cushion on our original is almost 10 pounds heavier than the cushion on the vintage one we just bought. The thickness is the same, but our original is MUCH more substantial and more comfortable.  The sofas were originally pretty expensive and well made (Hancock & Moore ball & claw Chippendale).  The new vintage one looks like it has been professionally reupholstered, and I suspect they changed the cushion.  I'd like to replace/upgrade it to come as close to our heavier original as possible.  I don't know if modern foam and dacron would do the trick --it almost feels as if our original might have springs in the cushion.  It's hard for me to tell (I'm an experienced seamstress but a novice upholster).  Any idea on what a maker like Hancock & Moore might have used for sofa cushions in 1990?  Thanks for the help!