I'm hypo-thyroid too and in researching the subject discovered that T4 is changed into T3 - the usable stage of thyroid hormone - in the liver. Thus it makes sense to make sure the liver is as clean and strong as possible. You may want to do some Liver Flushes - I just did a series of 3 and I lost 5 pounds - which on me is a pants size - and without dieting either, due to the holiday season. :)
to learn about the liver, these references are excellent:
Also, ***avoid tofu***. Soy sauce seems to be okay but tofu has things that inhibit thyroid hormone.