I invested in a tube of aquarium safe silicone and I have been going nuts with making decorations as I have noticed that absolutely nothing is ok for a betta. If it doesn't pass the pantyhose test, it certainly doesn't pass the paint staying on the decoration test.
I have been using glass stones and beads as well as marbles and they are so pretty! However, I just realised that they probably aren't food grade. Is that going to be an issue? I figured that they are probably better than paint leeching into the water.