What would a good thesis be for self-experimentation?

What would a good thesis be for the topic of self-experimentation?

That sounds dirty.

Well, the thesis has to come from your unique insight about the topic. You can't have a unique insight until you read a lot of articles about the topic, or gain insight in some other way.

When you ask what is a good thesis about it, you are really asking what is a good IDEA about it. So what is a good idea? Read until one comes to you. Search a database of professional journal articles for that topic. I don't even know what self-experimentation is... maybe like introspection.

Oh, I just looked at what self-experimentation is. So... if you are writing about a particular research method that involves experimenting on oneself, read some research studies that involve that method. You'll have a great idea while you read, and it will be your thesis.