In the interests of science, I offer you a summary of recent blood tests and conversations with a doctor. I don't know that I'm asking for any advice (but as always, huge thanks to the stars who support everyone so well) but perhaps this story and results might help someone.
This post is already too long, so I'm going to post the results in a 'reply' .
After many many years of to-ing and fro-ing, I started (apparently age-appropriate starter dose of ) Teva-25 last week, even before the blood tests were taken. One week down and I think I'm sleeping better and my head doesn't feel so stupid. I'll take the win this week, even if it's a placebo. He's scheduled a repeat prescription and repeat TFT tests in November. I'd asked him about mannitol/lactose free Levo but he said he didn't know and that I should speak to the pharmacist. Guess what, the pharmacist didn't know (and I had to show her how to read the box/ sheet info!!!). Anyway thanks to the info from here, I knew what I was after. I'll see how the Teva works out and ask to switch to Vencamil if I continue to have issues (at the moment I think it might be giving me a slight upset stomach, but I'm prepared to see if that fades/gets worse.
We also discussed anaemia and PA, he said to start with the Levo and then move on from there in some controlled way, one change at a time. My symptoms match hypo, PA, anaemia and we have a strong family history of PA/Hypo on one side, anaemia/B12 on the other. I've been having TFTs for years, because of family history.
There were a ruck of tests, with maybe 1 or 2 still to come in. He needed to spell out 'remember to do T3' but he didn't, so I'm going to try and get that done in the next round of monitoring blood tests in November. Also VitD.
My TSH is out of range high and he's confirmed to continue with the Levo (I never knew that you should stop other supplements, so results from previous years may have been suppressed by that). TSH was 1.74 in 2006, and has been creeping up since then.
My FT4 was 16 in 2006, has never been higher than 16 and has been down to 13.5
Serum Iron and Transferrin are low low low, so that may be next to address.
I really don't understand why my B12 is so high, so I'm putting it down to the story that 20-35% B12 assays can report high because of measurement/test kit features.
Low Iron/ B12/ Hypo/ VitD (etc) are so interconnected that I'm expecting to work on these for a while, and also see if I can of more to support my gut/processing - for me, everything seems to start with the gut/ food. I'm already dairy-free clean keto as my best way to manage digestive and other issues, and I expect there's a lot more tweaks/ refining to come.
Just one change at a time.