Here are books not directly related to Christianity and transgenderism but may be helpful anyway.
Raven Brangwyn Kaldera
Written by an genderqueer, intersex pagan describing the text as a workbook, it gives a variety of value. Foremost to me were about twenty accounts of hermaphroditic deities, mostly from the European continent. I had no idea there were so many. Like Eliade, I think that pagan gods are indicative of what humanity means to humans, and apparently transgenderism manifested through hermaphrodites is a large part of that. They also reveal the origin of transphobia and the power of being trans.
Every chapter contains discussion/personal questions, mostly genderqueer in nature, that are pretty meaty, though I haven't talked about them with others. There are a lot of interviews with religious trans people, mostly pagans but a couple Christians. They have a lot of identities and perspectives, but they all speak very positively, I almost say gratefully, about being trans. I didn't have much use for the last element, suggested hermaphroditic rituals, that seem only useful to pagans. Read an excerpt.
This is a short, self-published autobiography by Walt Heyer.
Before I came as trans, I was a flaming Christian feminist, God's Word to Women is the strongest weapon for any feminist arsenal. If nothing else, it will demonstrate how to biblically remove gender roles out of the gender binary. She writes an intense chapter "proving" that Adam was an androgyne which is still the most convincing case I've seen so far. The text is all public domain and online, including this particular chapter. Bushnell is, surprisingly, in all other ways a Fundamentalist Christian. I don't hold her writings as infallible as I once did.
Straight & Narrow seeks to give a calm and cool look at the issue of homosexuality in the Bible. Though it fails, I believe, and unequivocally denounces gays and lesbians based on Scripture, it's the best book I've encountered; for that I thought it deserves a mention.
The strength of this text is that it actually tells you in honest terms what its dissenters are saying about the same subject. That's brave. Many should learn from this! However, this is also a great weakness. When I was first questioning the condemnation of homosexuality by Christians, I should have read this book because it would have convinced me that it is no sin at all simply by becoming exposed to the alternate interpretations and watching the text fail to answer them properly.
I often have a naive faith that if Christians are just educated enough, if they actually listened to the right ideas, the truth would set us all free. This book proves me wrong and it saddens me. Even while articulating the pro-gay view, it fails miserably to answer it and sometimes I wonder if the author even realizes he is failing it seems so pathetic.