I believe also that the material has to be a special kind and I cant just use a normal seat cushion as a booster.
I'm not sure but I believe if the booster seat does not become a permanent fixture to the aircraft, there are no specific regulations about flammability of materials. It's just a piece of luggage as far as the law is concerned.
Unless the booster seat is made of specific dangerous materials (explosives, gas canisters, fuel and such) of course. Then the rules with regards to the carriage of dangerous goods apply. But I have yet to see a booster seat made out of explosive material.
In any case, at my club we have a stack of regular car booster seats and a few cushions in various grades of thickness, just in case we've got children aboard. None of these are specifically approved for aircraft use and I don't think anybody thinks they should be.
I have been searching for a booster cushion to both get me closer to the pedals and also to raise my height a little to see out comfortably.
Having said this, you might find that a booster seat by itself doesn't work for you. You might also want to search for some pedal extensions. Typically a booster seat will *increase* the distance from your bum to the pedals instead of decreasing it. Those pedal extensions do exist for various aircraft types but you've got to be very careful in attaching them. This made for some chilling reading:
http://www.aaib.gov.uk/cms_resources...BW%2009-10.pdf