After asking on mastodon, I finally decided to get an 11" MacBook Air from ebay for £89. It arrived and worked!
It's not super fast: quad core i5 at 1.6GHz, 4Gb RAM, 128Gb SSD and a battery that lasted 4ish hours. Unfortunately, a UK keyboard. I decided to install Debian bookworm from a USB stick. With no fiddling at all, I had a new system installed within an hour (actually less but I was on a work call for the whole time and didn't see when it finished). I did review what was on the Debian wiki but this was pretty out-of-date.
During installation I chose to just go with the Xfce desktop environment, as I thought GNOME/KDE would be too much for an older machine like this one. More below on memory issues.
- Wifi -- this is just a case of needing non-free drivers. Used instructions on stackexchange to get this working (add non-free repo,
apt update, then install drivers) - FaceTime HD camera -- this was more tricky, as there were several different sets of instructions, and needs a separate driver not packaged for Debian. The instructions here got it working though, and without a reboot!
I've been using the machine for about a week, while I've been visiting colleagues in Lancaster. So, no "serious" computing, but I did write this and an article for my website with no major difficulties. The unexpected (but should have been completely expected) issue is RAM and modern websites. The MacBook can play streaming video from youtube etc fine, but if you ask it to do that AND something else, things start to be choppy. I realised that I'd not setup any swap space, so perhaps that was the issue? Having completely forgotten about this part of setting-up a system, I consulted this guide and added 4Gb of swap in a swapfile (I didn't want to faff with repartitioning while away from home).
I'm not going to go on a tirade here, but modern websites SUCK. Even mastodon, which I'd have thought was better than many others, caused my computer to OOM and reboot when refreshing the feed of toots. Wondering if turning javascript off might be the solution? Anyway, stop doing that.