Joseph Fielding Smith’s 1922 book Essentials in Church History is now available in EPUB and Kindle. It’s a long book, which is part of the reason it’s taken so long. But it’s quite good and I think you’ll enjoy it.
A side announcement: starting now, all new MTP releases will use Kindle Format 8 (KF8) instead of the original Kindle Mobipocket format. (Older Kindles will still be able to read the books, but they won’t look as nice.) The reason for the switch is primarily economy of time — KF8 is very similar to EPUB and requires hardly any tweaks. The original Kindle format, on the other hand, is different enough that it takes a big chunk of time to make each Kindle edition. I’d rather spend that time releasing new books.