Is there a specific filler I should use as I have Hashimoto’s thyroiditis?

It is safe for you to have facial fillers with Hashimoto's.  Be sure to discuss your medical history as well as your goals for treatment with your injector.  There are many choices of filler and the appropriate selection is based on the area to be treated.

fillers will have no effect on your thyroid condition HOWEVER those with thyroid conditions metabolize fillers In different ways so HA fillers may or may not last a long and longer term fillers maybe bettter like sculptra, bellafill, and radiesse.  And plan to preand post treat your skin to avoid complications (see link to emeragecosmetics.com). See an expert.

There is no filler that would be contraindicated with this condition, nor Botox. I'd suggest a hyaluronic acid-based (HA) filler since it is reversible with the enzyme hyaluronidase, but other than that, Juvederm, Restylane or any other HA would be just fine for you. More importantly, see a highly trained & experienced physician injector such as a dermatologist to ensure optimal results & safety.

Fortunately if your thyroid levels are normalized and stable you can be treated completely normal and you should have no problems with getting filler. I would discuss your options with your local practitioner to choose the best options for your specific treatments.