ladyhelen - yes, what Kate says is absolutely right. My cousin had thyroid cancer 10 years ago, followed by other minor health problems (not connected to the cancer). By the time she was finally ready to start trying she was 38. After nearly two years of trying with no success she had one (failed) cycle of IVF, then conceived naturally a few months later. They lost the baby very early on, but then conceived again two months later, and now, after a very difficult few months, things have, touch wood, settled down and she is 27 weeks. She'll be just 41 when she has the baby.
Anyway, the point I'm making in my rambling way is that it is possible to regulate thyroid-related conditions (including not having a thyroid gland at all(!) as in her case). And also I think hers is a great hope-giving story for us all.
Kate - I don't think you're crazy. It's so important to do all the things that make you feel as though you are giving yourself the best chance possible for a successful pregnancy, as you rightly say. No point it driving yourself mad, of course, but you sound as though it's doing you good to be taking all the steps you are.
Have a lovely day, everyone. x