A further update on this topic:
I was talking this subject over with the guy at the bike shop, and he suggested that I try what he uses on cross country MTB, very wide, high rise bars, on a short stem.
Sounded all wrong to me, but he let me have a set to try on a “money back if you don’t get on with them” basis.
Well, having fitted them, I could instantly tell that I would need inner bar ends, so I fitted the cheapo copy ones that my other half bought for me from Amazon, transposing the L and R ones (I’m sure they’re wrongly labelled, either that or Chinese hands are different!).
The grip position is a smidge above saddle height, but not much. This is with a 2” rise, but that would differ for different bikes and these can be had in up to 70mm rise if you shop around between makes.
On test yesterday, they sailed past the two hours benchmark, where I usually start to find flat bars seriously uncomfortable, and still felt fine after four hours of bumpy old bridleways. Surprisingly (to me anyway), they work for climbing, and despite the short stem, they exhibit no twitchiness. The huge length makes them very good for negotiating rutted byways. No good for going quick on road sections, but that was never the brief.
This is the best so far!