There is also Two As One Princess, in which the protagonist is possessing a girl and they basically travel around the world doing isekai stuff. It's marked as gender bender and shoujo ai, but given that there is only one body and one of the two is a sexless ghost (uses female mannerisms early on to reassure the little girl he possesses, not sure about after that cuz I stopped reading after a while).

Is there a manga of this or is it just the novel?

by the way the sexless ghost was a guy before reincarnating.