I'm about to swap mine for an ADV screen and a set of Tobinators - Tobers does a kit for both standard 1150 and 1150ADV screens on 1100GS. Tickle the "Tobinators" link up there.
People will say CeeBaileys, Wunderlich, Ermax... If you search for "1100 screen" in "technical" and "GS Mods" it pops up a few discussions, none of which are any help in deciding what would be best. Motorworks did have a tall 1100GS screen in their last sale catalogue too.
Screens for sale appear fairly regularly on here so your options second hand are probably fairly wide. I too am fairly wide and need more shoulder protection, hence the ADV screen.
Check out the Wunderlich Vario screen. Also known as the MRA Vario. It's a 2 part screen which allows the screen height to be lowered or raised as desired. Do a search on either of these and you'll find quite a lot of people like em a lot.