Cult Sci fi - Man becomes female version of himself

[Rachael]

If I had to guess, I would say this was written in the 1960s/70s. It's maybe a sci fi adult fiction novel where a man goes on a journey. It's very psychedelic - there's a part when the man is turning into a woman and he notices the space between his breasts and the hardness of his breastbone and is surprised. There's another point when it seems as though the landscape is melting.

[Kate]

Very long shot:
I Will Fear No Evil by Robert A. Heinlein

A person, I think female, ends up with a man sharing her consciousness.

[SBC]

Maybe Orlando?

[stormhawk]

Excession by Iain Banks. later in publication date than your book, but it has some gender transform scenes.

[Trilobyte]

The Man Who Folded Himself

[Ann aka Iftcan]

While I don't think this is it, I'll still mention it: The Morphodite. The mc in this one actually changes himself several times.

[Cara's Craftsations]

The Female Man

[Joelle]

There’s a book called “If I Pay Thee Not in Gold”; it’s about a demon (not typical demons, it’s just what he’s called) who is male until he has sex with a woman, then he turns into a woman until (s)he has sex with a man. He finds a man and a woman that both fall in love with him/her, but they are never allowed to be with the other human. https://www.goodreads.com/book/show/1...

[Lobstergirl, au gratin]

Rachael, are you still looking for this or did you find it?