While others have mentioned the great GrapheneOS, I will throw two other options:

• CalyxOS — privacy oriented Android OS. While Graphene focus on security pretty much above all else, Calyx focus on privacy (and usability) more. Both essentially only target Pixel phones and are great choices.
• LineageOS + MicroG — AOSP fork, continuation of the old CyanogenMod, with an open implementatinon of Google Services. This is perhaps the most "normal" OS, seeing as Lineage's core is user freedom and not exactly privacy; however, with MicroG, you get a pretty private system with very few to none of the side effects of deviating a lot from standard Android.

Graphene is a great project, but I think it may be a bit too much for someone that is just entering the privacy world, hence why I'm suggesting these two options as alternatives that are less strict and "cumbersome" to use, so to speak, while not really sacrificing privacy.

In the end, as all things privacy, it depends a lot on your threat model, your tech proficiency and willingness to make "sacrifices" and adapt.