Thanks for the advice. Although the phone wasn’t for me, the process of choosing one made me consider what I would consider buying if I had to pick up a new phone in the near future.
I think I would consider a Fairphone, though only refurbished ones are in stock in the online store. In the UK, where I could possibly buy a new one, the vendor (The Phone Co-op) only appears to offer them as part of a plan, which I’m not interested in. I’m sure that Fairphone would do a good job of refurbishing old phones.
The downside of buying used phones, especially old used phones, is the lack of support for newer versions of Android, so the experience gradually degrades over time as I discovered recently when various web services dropped support for certain versions of TLS. However, if an up-to-date version of LineageOS is available then I understand that this problem is solved to a certain extent - at least, as long as there is a maintainer for the model of phone you have.
I’m already using F-Droid on various Android devices. Thanks for the hints about Aurora. It’s not something I would use, but it’s good to know that it exists.