It may be hard to find the success stories on here, as people come on here due to problems, especially when on T4-only treatment.
However, I first came on here with minor problems for many years, on T4 only, and growing problems as GPs starting harrassing me about my high level of FT4. As I felt obliged to try a lower dose, my minor problems became major ones, and I had to reduce my activity level to one I could manage. My blood tests stayed the same, so they harrassed me further. Doctors all ignored my low, or below reference range FT3. I insisted on a return to my normal dose as the "trial" of the lower dose was making me ill.
The good news is, that having studied everything I can find online about thyroid treatment, and having learned loads from this website, I finally bought T3 online without a prescription. It took a lot of courage to start taking it, but it has got rid of the symptoms I had suffered from for about 15 years. I am now healthier than I have been since before starting thyroid medication (following thyroidectomy).
My FT4 result is now always only mid-range, instead of being above the top of the range, and my FT4 is a little higher. All this is despite taking the same dose of T4 that I took for 15 or 16 years. It shows that my T4 is now being used more efficiently ie better converted as well as used once converted.
My endocrinologist is now asking permission for T3 to be prescribed by the NHS for me. He's not optimistic that they'll say yes, and neither am I, but at least he has learned from all of this. At the outset, he said he wasn't interested in my FT3 levels, but now he can see the difference that T3 has made.