Latest bloods:
fT3 5.8 (3.5-6.5)
fT4 15.7 (10-19.8)
(FSH is in overdrive, but since I was officially diagnosed with premature menopause today, that's to be expected.)
Given the 20% theory, I think that I'm now in an optimal place with the fT3.
Many thanks to all who have helped along the way, especially shaws and Clutter.