Ah! save-named-files (which you told me about before, but which I wasn't looking for then) seems to do exactly the right job. Thanks!
I know about the drop down on the right, but it's not that useful (except where you have so many files open you can't see them all on the tab bar). You can't, for instance, multi-select to close. So initially I thought I just wanted a better and quicker way to reduce the number - F3 in the tab bar works, but it just reduces the number and doesn't discriminate which files are being closed (unless you take your time over it). But then I realised I wanted a specific set so it's opening stuff as well as closing. Perhaps having a defined set depending on which part of the project I'm working on, and the xxx-named-files macros do that.