The ideal pedal for touring would probably be that flypaper pedal, it is only 4mm thick, and you stick to it almost as though riding in some binding system, but there is nothing. Unfortunately it is nor being adopted.
I use proper cycling sandals, and rat trap type pedals, I fabbed some metal sheet that goes over the top of the pedal so it does not dig in, Originally these pedals were designed to interface with metal cleats, not to have a knife edge bear on the sole of a casual shoe.