I work with TPE a lot for the hydration market. I would say that most synthetic TPE or TPU pretty much all of them give off some small amount of toxicants. So with your requirement of it being sustainable I was thinking of Natural Rubber (latex). It comes in a large arrive of different products and might fit your needs. I think it can be cast which is similar to how they make soft lures currently. With a layering pour system similar to how you make TPR parts for gloves and backpacks. Also silicone is a good choice but very expensive it might price you out of that market with the quantity you want to use. Also if you would like to save a lot on molded cost with silicone you can do a compression mold instead of a injection style. Also much easier to find a silicone compression molder instead of an injection molder. Good luck I am also an avid fisherman.