The Carolingian period sees the production of numerous works of writing. Frankly I am a bit surprised that you found it easier to find art than writing, given that the use of the written word is one of the central reasons why people call it a "renaissance."

There is quite a bit of poetry, a whole lot of history (both in the form of Annals and larger more "complex" histories), vitae (Saint's Lives), epics, theological writing, sermons, tons of letters, didactic works (mirrors for princes and the like) and more.

If you want access to primary sources there lots and lots of works in translation.

The easiest place to go would probably be Paul Dutton's Carolingian Civilization a reader that contains a ton of documents, ranging from letters to administrative works to poetry, history, etc.

You could also check out a volume edited and translated by Thomas Noble, entitled Charlemagne and Louis the Pious that contains the full works of several of the major biographers of Charlemagne and Louis, including arguably the most famous Carolingian work, Einhard's Life of Charlemagne but also a great (and very underrated if you ask me) epic poem about Louis by Ermoldus Nigellus. Notker's Deeds of Charlemagne is arguably written well after the bloom is off the rose of the renaissance but is still filled with lots of fun (largely ridiculous and anachronistic) stories.

For secondary sources there are many places to look but the go-to scholar for analysis of the written word in Francia is certainly Rosamund McKitterick. She tends to push very hard on the "writing everywhere" side of things (which some scholars would like to see tempered) but she is one of the most important Carolingianists around. A quick look through her bibliography on world cat or amazon will give you places to start.

Peter Godman is still the king of the mountain when it comes to Carolingian Poetry. He has an edited and translated volume of the stuff, Poetry of the Carolingian Renaissance as well as a scholarly analysis of how that poetry fit into the world of the Carolingians, Poets and Emperors

So yeah, start there and enjoy!