Will adding Goldfish to a tank of Pleco and Platy harm any of the fish?

I have a small plecostomus, three Platys, and I don't use a filter. I just change the water regularly. Yesterday, my sister gave me her four Goldfish. I know goldfish are heavy wasters since they dont have a stomach, and that will complicate having no filter, what else I have to do in order to keep all of the fish?