calibre can convert just about any format into KF8/azw3 (kindle) format. Alternatively, if you can make PDF with a 6 inch page size and tiny margins (I have no examples), you could do that. No jailbreak needed.
For sugestions on how to make the ebooks, try the E-Book Formats sub-forums
https://www.mobileread.com/forums/fo...play.php?f=177
particularly Workshop.
Provide information on the details of what you will be starting with.