Excellent thx for the update.I (test) fitted some leather seats from an alfa 156 in my bertone.
I think seats from a 147 are (almost) identical. They come in cloth, leather and shouldn't be to expensive. Without the height adjustment they are a good fit. I Also used the new seats rail and modified the attachment points.
If you want to give it a try, this are seats without side airbags and armrest.
Maybe it is not an option in countries where there are no modern alfa's .
I like them and it stays alfa romeo oem.