After posting on here and seeing a private endocrinologist who upped my thyroxine to 150mcg daily, sourced some T3 (Thylexan) which I've since taken. I havent been feeling great so was offered a blood test where they've checked my tsh, t4 and t3. These are the results
Serum tsh 0.01 (0.55-4.8)
Serum free t3 12.9 (3.5-6.5)
Serum free t4 17 (9.23)
My endo told me not to take the t3 as I couldn't provide a name if the drug at the time and he wanted to check again in 3-4 months. I don't want the doctor thinking my t3 levels are natural when I've been supplementing it.