As a starting point, I always recommend The Last Samurai: The Life and Battles of Saigo Takamori by Mark Ravina. No, it's not the novelization of that movie with Tom Cruise. It's very readable, interesting biography of a Meiji Restoration hero.

There is a connection to that movie, in that the samurai leader in the Tom Cruise movie is based off Saigo Takamori. And I figure Ravina and his publisher were quite happy to be able to give this academic biography the same name as a popular movie. :-) Helps sell books.

The Last Samurai is a really good entry point to reading about the Meiji Restoration because it tells one story: the rise and fall of Saigo Takamori, beginning to end, without assuming the reader already knows a whole lot of other stuff. That tends to be a problem with many quality Bakumatsu/Meiji Restoration books, they're not ideal places to begin learning about the era.

Also, given the particular novel that's sparked your interest, The Last Samurai is really appropriate, and will definitely give you more context for the novel. Saigo was the hero of the Satsuma rebellion, which happened the year after the Shinpuren "League of the Divine Wind" rebellion featured in Mishima's novel. And Saigo himself was a hero of Mishima's. In fact, Mishima fixated on Saigo's death in the weeks before his own seppuku.