Fairphone Open. It's the closest to the familiar stock Android from all options, but probably won't run on other hardware than the Fairphone 2.
It may not be LineageOS, but i think Fairphone Open is the closest thing to what you are looking for (AOSP without Google Play). It doesn't come preinstalled on a Fairphone, but it is officially supported and built for the device by the manufacturer.
It's been years but I've used and like Vector Linux - the light version requries Pentium II and 64MB RAM. The standard version requires a P3 and 128MB.
Vector is Slackware-based and actually pretty neat. With 512MB RAM I'd kinda keep my expectations low, though :)
I recommend flashing a copy of Point Linux http://pointlinux.org/ onto a USB using etcher. Haven't found a machine yet which it won't boot from. It is a discontinued distro with no further development but it does the trick for me in testing machines that don't have HDDs.
illumos is worth a mention then; it's a fork of OpenSolaris. Much of the top Solaris talent left after Oracle acquired Sun and moved to companies that contribute to illumos.
OpenIndiana is a ready-to-run distro moving to illumos, although it's still raw.
I normally wouldn't care about Solaris, but after having spent some time with its tools, I wish those ideas would spread more. rafekett is right, it is a killer server OS if you're willing to step beyond the familiarity of Linux, and hopefully illumos becomes more popular now that the OS isn't laboring under a single company.
Not exactly what you are asking, but just checking you are aware of the Fairphone2 and that it comes with the option to run an open source version.
>I ever do try Android again, it'll have to be running the stock OS, not a phone manufacturer's bloated interpretation.
If you ever do, go for the OnePlus. Not particularly for the hardware (though it's quite good). But their implementation of android is in my personal opinion the best. No BS bloatware, just an enhanced version of stock Android known as - Oxygen OS
The experience is comparable to my iPhone, it's great.
" Crafted exclusively for the OnePlus 8 Series, Live Wallpapers now connect to the OnePlus Weather app, subtly changing hues according to real-time weather conditions, bringing your smartphone experience closer to the environment around you."