tl;dr: I've used the Pinephone Pro running postmarketOS with SXMO for long trips and as a main phone for a while. I love the freedom the Pinephone Pro gives me to work with FOSS software for so many things and that it helps me to elude the smartphone doom spiral. I hate that I still feel bad using it as a phone ...
Honestly - using Sxmo on a PinePhone Pro is about as hard-core as you can go beyong building your own thing from scratch.
Ubuntu Touch on Pixel 3a, or Sailfish X on a supported device or a Librem 5 with PureOS even is a lot less geeky and more approachable thing.