It's my belief all that could exist is heavily bowdlerised because his wife was a proselytizing christian and burnt his diaries having declared he made a deathbed act of contrition recognising god. I don't think Burton's friends believed it for a moment, apparently she did a trick like cutting a vein to show blood still flowed, claimed she heard him speak and some friendly prelate agreed to the shenanigans in a higher cause. (Burton's abjuration of faith was obviously "political", for the religous fervour of the day)

It beggars belief a man who was into data collecting about prostitution and homosexuality, and who helped publish extensive pornographic works to a cogniscenti married a prude, and came to jesus at the last. But the thing is, he DID marry a prude. And he DID publish works which at the time were beyond the pale, and he DID explore the darker corners of british army life in the middle east and India. The only conjecture here is the deathbed confession of faith.

He wrote memoirs, for sure. "Personal Narrative of a Pilgrimage to Al-Medinah and Meccah" I mean, thats not objective writing by title-intent, is it.

No, I think I'm mistaken (and confusing it a little bit with the autobiography of Aleister Crowley, who was also something of an explorer and which I read around the same time - it is also interesting and untrustworthy but not as good overall IMO). I don't recall if it was the Farwell, Hastings, or Rice, unfortunately.