I reckon a cross between a quilt and a Neve style sleeping bag would be great. Maybe some flat domes to clip the underside sheet to the upper. So you can decide if you want to use the underside sheet or not. I used to run a EE quilt.
If the crowd in NN had been around when I bought I would have gone with them.
Also consider hi end synthetics like primaloft will be better in wet conditions.
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