I'm assuming there is no problem mixing FIMO with Sculpey, but I just thought I would ask. They appear to harden at similar temperatures. Is there anything about mixing them that could affect the properties of the medium?

mixing them works just fine. I mix classic with super sculpey and add a bit of black sculpey three to tint it. Keep it at 130 degrees C for baking, no problems.

adding fimo to super sculpey makes it a lot firmer and easier to cut detail in with, and also takes away the translucence

The new extra firm grey sculpey from midwest has very scimilar properties to a fimo sculpey mix too, although it does appear to be more brittle than the above mix if you need to discect the figure after baking.

here's two suppliers of EFG in the U.K.

polymer clay pit

gocreate workshops

hope that helps

seth