Yeah you don't post the trot at all normally. You also usually don't let the horses trot that much (unless you're trail riding on bad ground) because the tolt is so much smoother and more comfortable.
The standard Icelandic saddles are somewhat similar to the english ones. They look usually something like this: http://www.valhallaicelandic.com/_im...s_barri_tn.jpg
The most important thing is to have the saddle fit the horse properly though.
I'm now living in Scotland and I had to sell my Icelandic horse when I moved abroad from Iceland. I just got into horse riding again recently but this time around I'm forced to ride english style since I can't get at any Icelandic horses. It's been really interesting but I was a complete beginner in some ways because I'd never done posting before! It's also weird to not have any tolt to work with.