Mary, I recently switched from SPD's to the Look pedal for exactly the same reason. I tried different insoles for my mtb. shoes, helped initially then foot started to go numb right where the clip came in contact with pedal. Went to the Look pedal not too long ago. Really didn't solve the issue, ended up putting new insoles and some shim that came with the insole into my new road shoes. Once I put the shims in I've had a lot longer of a ride before, if any, numbness sets in. THe shims came with my specialized liner. I put the shims in my mtb. shoes also but haven't been out in them yet to see if it will make a difference or not. Give that a try first. Maybe that is all you might need and also to loosen the straps to the shoes, that also helps for me too.