The rear panels of the seats are already non-wool? I would just keep it that way. You cannot really appreciate the carpet in the footboxes. They are so low, dark, and deep , you can hardly see it and that is the bulk of the carpeting. The tunnel is the only place you would "feel" the carpet, and you would see it best on the tunnel and on the trunk panel behind the seats. IMHO, I really do not think it is worth the extra cost for those two areas. I would just do what you feel will make you happy and not make you have any regrets on a build you have put so much into. Me personally, if I was to do it over again, I would still choose the
synthetic.
I would take Patrick's advice and get some carpet samples.