OK, so massive improvements in the SSD swap write activity. Running uptime shows 2 days 7Hrs with 42Gb written. Same kind of activity as before, general web browsing, website management, Word etc.
I've been using Edge with the tab discard, switched off sharing, and all of Spotlight except Applications. Followed the suggestions from
@TheSynchronizer (hat tip) regarding some deeper keep awake threads as I was finding a lot of activity was happening overnight during the MBA sleep. Use 'sudo pmset -g assertions' (from an admin account) to see what's keeping it awake. See my posts passim as to the details.
I may go back to Firefox as Edge is a bit odd but other than that I think with the help on this forum the problem is cracked!