Gender Fluidity books recommendations

Hey everyone,

Can you recommend some books with the specific on gender fluidity?

I'm a transgender person, who read a lot of books about transgender matters (non-fiction/ fiction). I have a friend, who struggling with their gender identity. There are not consider the transitioning. They like their assigned gender at birth, but sometimes they like to express themselves not femme, but masc and vice versa. They want to understand themselves better. But my experience is different from their. I understand of how the literature gives an amazing understanding ofany things, when I compared my journey.

So, I tried to find for them the books related to gender fluidity topic. I have read Paul Takes the Form of a Mortal Girl, which is kind of related to this topic, but I try to find something like Whipping Girl, but in gender fluidity matter. I think about Judith Buttler, but it will be super complicated for the beginning. For me Buttler is always about paper, pen, and notes, which require a huge attention and little bit understanding of the gender identity topic.