My shop has a concrete floor, and it used to cause me some back and leg
problems. I started wearing some slip-on's from Lands End a few years
ago, and they have been great. Thier catalog no. is #09270-8AGX , and I
just ordered another pair for 29.50. The slip-on feature is especially
appreciated by my wife, since it makes it much more likely I'll take
them off when I come into the house.
Land's End offers some orthopedic inserts for various foot shapes, but
I've not tried them.

I've also been using a couple of the shock absorbing mats from
Woodcraft at my lathe and workbench, and they help as well.

Ron