Sounds tricky! Have you already discussed your thyroid issue with your fs? It may make a difference to your treatment.
I would always try to stay as healthy as possible leading up to and during a cycle. In terms of diet, basic 'healthy eating' is all you really need. The cycle that finally worked (9 attempts for us!) We both went as healthy as possible for 3 months leading up to the collection (it takes about that long for the sperm to develop) So no alcohol for either of us (DH hated that one ), no coffee, soy, or takeaways. Lots of fresh stuff, full fat dairy, lots of pineapple. We also tried to up the exercise, but that was a bit harder to maintain!
Good luck!