I'm just an interested spectator sitting by watching your progress. I did a scratch build of this car a few years ago on another site and of course I ran into the same problem you are dealing with about getting a decent looking fabric for the seat. My wife, who makes quilts showed me a cool idea which might help you.
I found that Mercedes has reprinted this fabric in several colours and I was able to download a good quality image of the Moss' blue. I massaged that image in my photo editor till I had it at the correct scale for my 1/18th model. Here's the cool part. Here in Canada you can buy what's called wax freezer paper used for wrapping food to be stored in a freezer. My wife showed me that a piece of fabric can be steam-ironed onto a sheet of it and it will adhere perfectly and I assume the wax surface melts just enough to bond to the cloth.. Now you just trim that piece of fabric/wax paper to an A4 size and it can be run through a printer and have the image printed on it. I suggest you try a very tight weave of fabric to be closer to scale. It works a charm.
Here's my fabric ...
Hope this helps.
Albergman