Change Apple Watch altimeter units

I have always had the elevation on my Apple Watch Series 6 set to metres. Since updating to WatchOS 9 a few months ago when it came out, it changed to feet. I didn't do anything to change it, it just automatically changed as I updated.

I've searched online, as well as here on this site, and the solution is apparently to change your region (Settings, General, Language and Region) to a country that uses metres. Well, I went to this setting, and it was already set to UK (like it always has been), but still showed feet. I changed it away to US and then back to UK to see if that would work, but it didn't.

There's a few things that are really frustrating - firstly, that it changed just with a software update. Also, that the setting isn't just "units - metres or feet" like it is in workouts (you have the option to record workouts in miles or kilometres, for example - it isn't tied to your region).

So, any ideas anyone? What do I do? I live in the UK, we use metres in the UK, I don't want to change my region to something other than that because that's not where I live, but I want my altimeter to show the elevation in metres.