So, i've finished all the interior of my truck now, stem to stern of the
cab was sandblasted, fiberglassed, primed, covered in thick
undercoating, and topped off with a nice new carpet.

Which brought me to the seats.  The drivers side seat was trashed, (both
the fabric and the foam) - and then it dawned on me, i've had a pile of
black leather hiding in my closet for the last decade, and i think it's
time to bring it to good use :)

So i'm thinking, black leather seats, with one of those back
massager/heating cushions put inside the seat before it goes back
together, and the most /absolute most/ soft cushy foam i can find to
replace the standard foam that comes from the factory.

Basically, you know those 100,000 high end sedans with the ungodly
awesome leather seats in them.. i want to make some of those for my truck.

The only part of this that i need help with, is figuring out how i can
make it ungodly soft and squishy to sit in.
1) What specific types of foam do i use for this?
2) Do i use just one type of foam, or do leather upholstery
professionals use combinations of secret things to make the ultimate
comfortable seat? :)
3) Do any of you know any sites you have bookmarked which discuss these
types of questions - and can you share them with me? :)

I've done some asking around locally, but aside from using 'sewing foam'
which is necessary for sewing to the leather -  and then 'rebond' foam,
(which is not comfortable) they almost always use the pre-existing
factory foam, and just cover the seats with the leather. (which is what
i don't want to do)

thanks,
James