Having got a 1 year multiple entry OA non immigrant visa 18/9/2019 from London with help from this group a quick update.
I returned via Suvarnabhumi airport yesterday no questions or insurance required at this time[immigration quietist I have ever seen it).
In about a month flying out to Perth and returning to Chaing Mai Airport if I get a problem anywhere re Heath insurance maybe it will be here but I’m hoping not.
On advice from this group I plan to get a re entry permit in Chiang Mai before I leave Thailand in April and use that to return in October.
I will keep the group updated.
Thank you to everyone for the help.