I also suffer from numb feet. I have a problem in my left toes that physio is unable to identify but feels like trapped nerve and jangles and goes numb. I'm training for london marathon so have been increasing my mileage and last week both feet were numb across toes and front pads. Have recently bought new trainers and after testing my old trainers and 2 new sets (which both seem to give me numb feet) have indentified that the toe box in my old trainers is far more roomy and whilst new ones are snug and bouncy I'm sure they are leading to compression. The trainers are half size bigger than shoe size but the design is more snug and narrow on top end of feet.
Next experimen for me is to do a long one in old trainers and test. I will the have to consider whether to get yet another pair of old trainers which were K Swiss jetsters which aren'tas cushioned as some of the more expensive cushioned types or research designs of other trainers.
Have been looking this up on various sites and others recommend stretching muscles in foot by sitting with feet flat against wall dropping chin to chest and stretching forward. I haven't tried it yet as will leave that for after next experiment.