I got an aluminum baking tray from my grocery store and used it for the purpose you’re looking for. It’s thicker than foil so it can be used a bunch of times, it’s also malleable so you can adjust it with you hands to take the shape of the bottom of the air fryer, I also put it in the dishwasher to clean when necessary. I attached an Amazon link, but you can buy them 1 or 2 at a time in you’re grocery stores baking section