I know exactly what you mean! It took me forever to find cards for my therapist. I have given her two. My friend also recently had trouble finding a thank you card for her therapist. It is hard! They are either too basic or too friendly or too mushy. I ended up using cards with quotes on the front but blank inside for both of the ones that I gave to my T.

Good luck finding one! It will take some time, but you'll find the right one. I think it is so great and kind of you to thank your T. I don't think they are thanked enough.... People are quick to complain and blame and not so quick to thank appropriately, in my opinion.