A peeled zucchini or a peeled carrot provide different shapes/firmness and an option to carve your own piece, of course just throw it away after. The natural sliminess of the peeled vegetable can also help insertion, but that's debatably not what you're looking for.
The best option is, of course, making some money to buy a medical grade silicone one, that will last you a very long time, but hey, I don't know if you can get a job at your age ;)
