The obvious choice is to buy a Yamaha pedal. If you like the look of a piano's sustain pedal, get a
FC4. If you just want a square thing on the floor, get an
FC5. Most generic pedals will work, too.
For my Tyros, I use one of each. The different appearance means that I know which one is sustain and which one is whatever else I want a pushbutton to do. But the Tyros also has a third pedal jack, which I use for a volume type pedal. The 910 only has two pedal jacks, so you'll have to decide if you want two on/off type pedals, or one on/off and one volume, or two volume pedals.