Pedals with largest outside platform area
Something like the Crank Bros Stamp pedals might work. The large version are recommended for people with size 10-15 feet, and they also have metal pins that stick out allowing your shoe to grip onto the pedal better. 

It might make sense to go to a local bike shop to see what help they can give you. Seeing the pedals in person might let you know if they can work. Or they might be able connect you with someone in your area that modifies bicycles for people with mobility issues.