OK. The previous idea I posted was satisfactory but I've moved on!
A month after receiving my first Ashbory (my partner lives 100 Km from me and I wanted one in each house - extravagant, I know) my second one arrived.
I had bought a D'Addario Acoustic Quick-Release attachment trying another suggestion for playing standing elsewhere in this forum but didn't like how it worked.
With the second Ashbory, I also bought the $4 strap sold by LargeSound. I investigated the Quick-Release once again and after little time found that If I attached it to the top of the neck and the adjustment buckle, I could get a very stable three-point support which keeps the Ashbory in a perfect playing position for me.
The photos will clarify things.
Should have bought two straps, not one - one for the other Ashbory!