Help me thank my dad*

Here's a low stakes question to start the community.

My father adopted me when he married my mother forty years ago. Unfortunately, she died only seven years later. Together they had two of their own. He's not an overly affectionate person, but in my adulthood he's been incredibly supportive.

Recently, he took a week off of work (a BFD for him) and flew halfway across the US to take care of me and my animals after a serious surgery. I'm trying to write a thank you note, but everything I write seems clinical or soppy. I've even tried chat GPT, but they're as awful and stilted as I am.

So here's the thing I want advice on... How do I thank him for continously choosing to be my dad for the last ~40 years?