Arch Molds insoles(Blue model) have a fairly stiff sole if you do not put them in the oven to mold to your foot. Can be found in running specialty stores. Not cheap at $40+ a set. I use them in my cycling shoes without heating and they work pretty well. Have Mortons Nueuroma on one foot and need a stiff insole.

You may be better off saving up for a pair of road shoes.

I would agree that if you have numbness that soon you need to loosen something. Maybe the toe cages are binding your foot.