http://www.lynplan.com
watch all their videos on you tube
it's in English, from traditional to product development, from hair to foam and anything in between
I am certainly no upholsterer but I found some really interesting information in those videos. As I said, I am no upholsterer and therefore cannot be too offended by whatever cursory attention some important detail is accorded in the site you linked. "Where ignorance is bliss..." 'n' all that jazz.
I enjoy the puzzle of slipcovering and noted some interesting arrows to add to my quiver. The grim reality of my very small (read: nascent) business is that I have to keep myself "busy" and that means figuring out how to be competitive with respect to price in an area not so full of "well heeled" customers as I'd like!
It ain't always easy, Bruno!