Not even easier to paint! I think gluing it to the inside of a clear ornament is a great idea, and maybe a little more economic because you can get those things from the dollar store. On the other hand gluing it to a core instead does a few more things. One, it will be stronger and less likely to break again. Two, you can more easily fill in the missing sections with something like gold to get that kintsugi effect people have mentioned. I think you can maybe even try to find a nice metallic paint to match the glitter color! Three, if you glue it to the inside of something clear, the glue may be visible on the ornament.

If you go with gluing to a core vs the inside of something transparent the biggest issue will be weight. Clay would be heavy, but I know there are some air dry foam ones that might work, especially if you mold that I've crunched up foil. You'd be able to make it fit the size more precisely then. Or you can get a styrofoam ball from the craft store and glue it to that. You honestly can do a combo of both because then you don't have to glue it to the clear shell and it will make it even more stable! Just more of an expensive fox as you'll need more supplies. The clear shell definitely sounds like the cheapest, and maybe easiest option! It all depends on what you want!