MrFinigen

If you are still backing the idea of an origin story, i would strongly recommend it. It is a very well loved book and has the basics of a Maul origin story, while also allowing the freedom to expand where you see fit. It also explains the processes by which a master tortures his apprentice to make him a Sith. It is important to note that in the book Maul is being trained by Sidious while he is still an apprentice to Plagueis, and Plagueis isn't actually killed by Sidious until well into the events of The Phantom Menace. Because of this you can not only expand upon Maul's pre-TPM character, but you would have an opportunity to flesh out Plagueis in the new canon, something that fans would greatly appreciate.

Have you read the novel Darth Plagueis? While not canon anymore, it does have a Maul origin story that could be re-appropriated into a game to fit the new canon.