Interesting choice, using curved stators. I wonder why though, for the purposes of a headphone in which the driver is sitting right next to the ear dispersion shouldn't be a problem. Of course curved stators create odd problems with tension unlike as you said, he uses a large amount of tension. In which the bass disappears. 0.95 definitely seems on the thin side, though apparently the HE Audio Jade uses 0.5? I'm definitely going to have to defer to spritzer, who knows everything there is to know about electrostatic headphones, but otherwise say 2-4 microns is a safe bet, with something closer to 2 being preferable. spritzer would also know about where to buy mylar in Europe.
This person used 1.4 micron: http://www.head-fi.org/forum/thread/498095/review-refurbished-micro-seiki-mx-1-electrostatic-headphones-ms-2-headphones-mp-1-amplifier