Sorry, I pontificated but didn't answer your question.
If your TSH and T4 are normal but your T3 is low, then it may be...just maybe....very good but in combination with thyroxine.
Is there such a thing as low T3 syndrome requiring T3 replacement only? That is the great medical debate. Me? I think that in that case there may well be a case for combination therapy T3 AND T4.