Paper straws are horrible, I don't think they should be chosen as a counterexample to skepticism about biodegradable materials.
Another option would be to buy canned beverages rather than fountain drinks.
Because of the small amount of plastic in each can, and the high heat of the smelting process, odds are good the thin plastic liner will be almost fully combusted, which should greatly reduce the amount of microplastics.[1]
1: https://www.sciencedirect.com/science/article/abs/pii/S03043...