Instead of tossing your extra starter add it to discard recipes. There are so many things you can do with that extra sourdough starter. My other tips is to keep a smaller amount of starter. Instead of feeding 100g of each flour and water, only keep around 25-30 grams of starter. This will significantly cut down the amount of waste. Then, when you're ready to bake bread, up the feedings until you have the amount you need.