You may want to try Candidase by Enzymedica. It deals with candida overgrowth pretty good while minimizing die off reactions, so your kidneys won't get stressed even more.
The key is to restore the good flora so your kidneys can heal. You're right, any detox will bring stress on the elimination organs, and that includes the kidneys. Measures to help with this are low animal protein intake, activated charcoal, enemas, herbal teas specific to kidneys, and fresh juices like lemon, celery and cucumber.