Any recommendations on where to test my T3 & T4 as NHS don’t pay for it

Can anyone make sense of these? I asked for T3 testing however they were unsure how to test it.

How often to use them? Especially for people like myself who are inside 90% of the time. Maybe 2-3x a week?

When and how do I use it?

If my cholesterol is high (5.7mmol) and my thyroid stimulating hormone (TSH) is low 1.1mU/L; meaning my body isn’t needing to signal to make more thyroid hormone, is my underlying issue still hypothyroidism? Could I be running on cortisol instead?