Looking for low-level night lights (not interested in plug-in ones),
most seem to have their own mounting frames, or metal clips into a
plasterboard hole that I could see working loose.

I found these that fit a standard back box, which I'd prefer

https://www.eterna-lighting.co.uk/product/rwl15

Rather than just white, are there any manufacturers who include such
lighting to match other colours/finishes for their ranges of
switches/sockets?