Hi Russ,
I'm also in the UK, as is Jeff.
I bought some A3 paper but only 200GSM and it is to me just thin and no rigidity at all.
So for the R1900 should I be looking at at paper/s in the 280/300 GSM mark?
I use Ilford Galerie Smooth Pearl for A3 competition prints, that is 310GSM, one of the heaviest papers I know. Even so, I use a 200gsm backing fixed with spray adhesive before mounting the print. I hate to see wavy prints in a mount!
Ilford papers are competitive in price and the thinner versions are cheaper still.
One modestly priced paper I use is Epson Archival Matte, 190gsm. A very nice matte paper which I have used for competition, again with a backing to stiffen it. It has the advantage there are Epson printer profiles available for it.
Terry