@dandelion
Hi dandelion,
From what I've learned about Commodore Monitors on the
Big Book of Amiga Hardware Site a Commodore 1942 monitor would probably be your best bet. It handles a range of frequencies and I believe can handle AGA "double" screenmodes (I'm sure someone here can correct me if I'm wrong :-) ). More common monitors like the 1080 and 1084 don't seem to be quite as capable when it comes to AGA.
Hope that helps :-)