I used 3/4" but your supposed to use 1/2" foam, I would not recommend the yellowish-white upholstery it eventually gets flat and useless. Worst case get a yoga mat, it about 1/2" thick. I used a black dense foam called ensolite, some people claim not to use it but it works great, my butt don't hurt after a ride. It's priced by the foot but you'll be able to do about 6 seats.
http://foammart.com/closed-cell/ensolite/
For the leather I used theleatherguyofmn on ebay, bought a skin and it was about enough to do two saddles. I like his sales as he shows the actual pieces your going to get as opposed to a stock photo
As far as shaping the foam, I used an 80 grit wheel on an air die grinder- care not to cut in too quickly.
I used Dan Tack upholstery spray glue to get the leather down on the foam, BTW I glued the foam to the pan, shaped it, then laid the leather down and around the edge. make sure to bend the foam over the edge and shape it down or blend it.
Here are my pics, I actually don't know what seat brand this is, but it's a wider one and was comfortable without anything, even more so now. I didn't have wear tabs, but who cares.