IMO, your foot numbness can also be attributed to the low cadence. If you are grinding away, pushing down on the pedals instead of spinning and focusing on using your entire leg you could be putting quite a bit of pressure on your feet. When pedaling try thinking about "kicking" your lower leg out using your upper leg and see if it makes any difference. that may be confusing but think about the walking motion which typically doesn't involve smashing your foot down onto the ground