Okay; this thread will have some spoilers and info of the light novels!
I have not read the novels yet, just the manga and some light novels summaries. Till now the Light Novel series has 8 volumes and is still ongoing.
The Light Novel series is written by Ishida Rinne and illustrated by Okiya Ichiko. It even has its own trailer.
Volume 1. "Okobore hime to Entaku no Kishi" (--It's pretty much the very first volume of the manga, but of course with a lot of extra details!
Volume 2."Okobore hime to Entaku no Kishi - jou no jouken (aka. the requirements of the queen) "-- This was an aborted arc in the manga. I have no idea why the mangaka did this; but the manga isn't covering it... they completly aborted the Guido arc; darn it!!!
Volume 3."Okobore hime to Entaku no Kishi - Shougun no Yuutsu (aka. the melancholy of the general)".-- This one is about the second arc of the manga; which you'll be able to check out very soon!
Volume 4."Okobore hime to Entaku no Kishi - Shōnen no sentaku (aka. the election of a boy).
Volume 5."Okobore hime to Entaku no Kishi - Ōji no ketsui (aka the determination of the prince).
Volume 6."Okobore hime to Entaku no Kishi - Kunshu no Sekinin (aka the responsabilities of a ruler).
Volume 7."Okobore hime to Entaku no Kishi - Kotei no tanjou (aka. the birth of an emperor).
Volume 8."Okobore hime to Entaku no Kishi - Hakushaku no kirifuda (aka. the trump card of the earl).