While baking soda and washing soda are two different ingredients, and the original recipe calls for washing soda, both are safe to use in the laundry. In fact, baking soda boxes often give directions on how to use it as a laundry additive, and you can include it if you choose. Some people add salt too. But if you're trying to save money, why add more ingredients than you need. By the way, if you're really short on money, just use any leftover slivers of soap in place of the fels naptha. You can avoid the borax and soda too. A lot depends on your water type...