Hi Dani,
It depends a lot on where they are at - do they see through government lies and wokeness/gender ideologue stuff? Covid? The war in Ukraine? 9/11? How actively are they searching for answers? If they are at least critical about any of the mentioned topics, but aren't ready for The Wave series, maybe a good place to start would be the Ra material/Law of One, as they were first to introduce the topic of densities, as far as I know. Of course, the concept of a multilevel Universe goes back much earlier, even if not described specifically as densities, so if channelled material is a bit "too much", perhaps some books about mythology or that expose how the historical record has been corrupted and the materialist/Darwinist paradigm is completely wrong?
Some suggestions:
Mind & Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False - Thomas Nagel
God Exists But Gawd Does Not: From Evil to New Atheism to Fine-Tuning - David Ray Griffin
Darwin's Black Box - Michael Behe
Genetic Entropy and the Mystery of the Genome - John C. Sanford
The Science Delusion/Science Set Free - Rupert Sheldrake
The Field - Lynne McTaggert
The Crack in the Cosmic Egg - Joseph Chilton Pearce
Secret History of the World Vol 1. - Laura
The Secret Teachings of All Ages - Manly Hall
Views From the Real World - G. I. Gurdjieff
The Fire from Within - Carlos Castaneda
The Caricature of Love - Hervey Cleckley
Hostage to the Devil - Malachi Martin
Paul's Necessary Sin: The Experience of Liberation - Timothy Ashworth
Anything by Mircea Eliade or Joseph Campbell might be worthwhile too, depending on their interests. Hope this helps!