A thoughtform can be based on many things. However, many experienced practitioners in such areas will warn against giving one independence, or even a personality, for many reasons.
Any thoughtform may work outside of the magician, but it exists only within the mind. The mind of the mage is the central server, so to speak, and keeping a servitor active takes mental resources. Giving a thoughtform too much of a personality or individuality means it becomes taxing to its creator.
They also require an investment of energy to even exist.
Many warn of a servitor getting out of control, and causing harm to its creator.
Therefore the advice is that any mental construct is created for a specific and brief task, then promptly destroyed immediately upon completion.
If you watch Rick and Morty, a Mr. Meseeks is a perfect example. The longer a construct exists, the more it demands, and the more potentially harmful it becomes.
Before I forget, libromancy is a misnomer, at best.
The suffix -mancy denotes specifically divination:
Cartomancy is divination using cards.
Pyromancy is divination by interpreting shapes in fire.
Necromancy is communication with spirits of the dead, by means of divination. The term is a little bit of a stretch, but understanding that it is communication with spirits, and not raising corpses, becomes important.
There is bibliomancy, which is divination using books. The most common method is to use a thick book, and by some means choose a random page. The first place where the person's eyes fall is the answer to the inquiry.
As for libromancy, all I find online is directly associated with recorded music, and with works of fiction. I would not suggest using fictional novels as a source of anything other than entertainment.
Not everyone considers a servitor a mental construct; I have always found them to be energy constructs that can (and in my case do) act and interact without my interference. I gave mine, for the most part, a sense of personality and independence so perhaps I got more out of mine than you got out of yours prsona.