I know what you are going through as I have also. I am now trying to find a material and going through all kinds of misery.
I have used Belleglass material in the past with GREAT success. It is a crown material and the Dr who uses it, uses HOLISTORE as filling material. I am highly allergic and this works for me.
the clincher is that the color is not natural. The holistore is very white and the Belleglass crowns are a very bluish white and not natural looking. It has no barium, no metals or metal oxides. It is made out of methyl methalcrylate, I believe. I am a highly allergic person and it works great for me.