The one downside of the higher resolution camera was that it eats batteries.
So, after experimenting with one or two cheaper solutions that just annoyed me, I have gone for this. A Zoom Q8 Video Camera. I picked it up second hand, but in excellent condition.
Post from RICOH THETA. – Spherical Image – RICOH THETA
However, the price of specialist conversions have been coming down recently, and for 80 quid I could have the internal filters removed to turn it into a full spectrum camera. This would let me use it, with appropriate external filters, both as an infra-red camera, and for astro-photography with better response in the Hydrogen Alpha band.