A bus (buses) from Füssen/Reutte to Zürich or Luzern is likely to be more complicated then the train.
The Bahn query webpage has an English language side. If you learn a little bit about the geography and how to spell the town names in German, it's not difficult to navigate. Hint: spell Füssen, "Fuessen", and Zürich, "Zuerich".
About the "best" (price, time, and number of changes) connection I find between Füssen and Zürich is an RE from Füssen to Buchloe, and EC from there to Zürich. With advance purchase and commitment to a train specific ticket, you can get fares as low as 49€/pers.