This makes so much sense! I wish I knew this before.
As far as I know I have never had my T3 or thyroid antibodies tested (is there a name for that test?). Is it something docs will do easily? I have an appointment with my GP on Saturday to discuss this in detail and will request a T3 test, as they want to retest my TSH4 and T4 in 3 weeks time.
I was diagnosed with and under-active thyroid within the same week of being told I was type 1. The consultant literally said it’s nothing to worry about just take this tablet daily. When you have just been told you have to take multiple injections daily for life... the one tablet (which I know affects me in so many ways) was the least of my worries.
Sadly, because it has never been an issue - or has been stable I have never worried about it. My situation now has forced me to pay more attention to it. (Feel silly now thinking about it!). But hoping it wont take toooo long to get my head around it.
CranberrryIce, I can completely understand your view of your thyroid issues, when you had to wrestle your T1 into submission at the same time. I was fortunate enough to be meds-free, forever, before my Levothyroxine, so you can probably appreciate I approached it with some reluctance and some enthusiasm, because I didn't want to be taking meds, but was buoyed by the prospect of my unpleasant symptoms would go away, or at least ease.
For me to understand things I tend to try to visualise things, and my explanation to you was pretty much how I got the hang of it.
Moving on to you though: On the NHS, they are very reluctant indeed to test FT3, and bearing in mind you are T1, I would be astonished, due to the commonality of auto-immune thyroid disorders amongst T1s if your antibodies hadn't been tested at some stage. Do you have access online to your test results? If you do, you would be able to track back on what had been done.
Moving back to the FT3 testing, whilst your TSH (and T4) are in range it can be a real battle to have FT3 tested at all. My initial thyroid panels were requested by an Endo, along with 20-odd other tests. He was,.......... erm,.......... trying to work out what was giving me some bonkers weird symptoms - and failed.

Anyway, you may find yourself with better access to the detailed testing, due to your close monitoring in your pre-conception stage.
The tests can be done relatively cost-effectively, by places like MediChecks, and on Health Unlocked there are quite often discount codes on Thyroid Thursdays (I kid you not!). In your shoes, I'd try to have the NHS do them, as then you'll have consistent lab assays and be able to track your trends, but Medichecks, Blue Horizon and others are all out there, more than happy to test whatever you want, within reason.
https://www.medichecks.com/thyroid-function-tests/thyroid-check-plus
I'm so glad you had a look in Health Unlocked, because I really did find them very helpful, even when I was asking very simple, and some rather left field questions. I'm glad you're finding them useful too.
Let me know if I can help you further, but otherwise, all the best with your big adventure to expand your family. Exciting times!