I Will Fear No Evil by Robert A. Heinlein
"Johann Sebastian Bach Smith is very old, very rich, very stubborn - and caught in the medical straight-jacket of extensive life support. So he conceives of having his brain transplanted - whether the operation is successful or not, he'll at least escape the straight-jacket. So far, an idea done many times before. Now Heinlein adds his own touch, as the 'donor' body turns out to be that of his young, extremely beautiful secretary, Eunice Branca, who was mugged and murdered. When Johann wakes up after the operation, he finds Eunice there in his head, ready to help him adjust to the new world of being very much a female. Is Eunice real, a product of 'body experience'? Or just a figment of Johann's imagination? Heinlein lays clues to this important question throughout the book, but you'll have to read it and make up your own mind"
Old TG book I read years ago, deals with multitude of aspects in regards to TG, if you can read, you should read this...