Good luck with your project. My project is a bit easier, since the floor of my A is flat. My base is sheet metal lined 3/4" plywood covered with 1/4" aluminized foam with Masonite on top of that. Then I laid down some padding that is aluminized fiber on the bottom and 1/2" of mixed fibers.
I got my carpet from Kristkustoms. I ended up choosing a nylon based product since so much of my cab is taken up with seats and most of the rest will be covered with a floor mat of matching carpet. There isn't much space in an A coupe and I just couldn't justify the admittedly nicer wool when I would be covering so much of it up. You might also try American Trim and Upholstery Supply(www.atrim.com
Finally, I would strongly suggest looking at "Custom Auto Interiors" by Don Taylor and Ron Mangus. It has a very good section on fitting a carpet over a trans tunnel. I would suggest looking up the ISBN number on Amazon (and you could order it or look for a used copy, too) and then asking your library to get it on inter- library loan. Then you could review it and see if you wanted to buy it or copy the pages you needed.