First of all, do you have any symptoms? Fatigue, facial bloating, cold sensitivity, constipation, crashing in the afternoon are the most common symptoms.
Free T4 you want to bring up to +1.6-1.8 ng/dL, contrary to internet dogma, Free T4 is correlated to well-being, not Free T3. (
https://academic.oup.com/jcem/article/91/9/3389/2656451)
The physiological ratio of T4/T3 is around 10:1. A healthy thyroid produces about 100 mcg of T4 daily and 5-8 mcg T3 through direction secretion. A further 25 mcg of T3 is produced via conversion of T4 to T3 for a total of 32 mcg per day (direction secretion+conversion).
You want to get your Free T4 up to 1.6 ng/dL at least, if still symptomatic, add 5-15 mcg of T3, starting with 5 mcg at a time.
Most important question is, what are your symptoms now? Even without symptoms hypothyroidism is a big risk factor for atherosclerosis (plaque in the arteries) which is a big risk factor for stroke/heart attack.
People will erroneously tell you that T4 is "inactive" that RT3 blocks T3 receptors and that only T3 is the active hormone. All three statements are completely false and not how thyroid physiology works. 1. T4 has it's own functions independent of conversion to T3 (just like GH works without IGF-1 in certain processes) RT3 IS inert and does not block any receptors. T3 needs T4 to work, some tissues need T4 to convert themselves and are poor are utilizing serum T3.
You will see many symptoms unresolved in people who only take T3 without T4. I've had patients on all thyroid meds (T4/T3 solo or combo and dessicated pig thyroid). Most patients feel great on T4 only IF we go by Free T4, not TSH like most practitioners do. Treating thyroid by TSH is like doing TRT without testosterone tests but using only LH/FSH as your guide. Zero sense.