Thanks for all of the replies!
Lots of info and suggestions to think about there.
I hate that I sleep cold - it means that I'm always carrying more insulation than I would like. Whenever I read blogs or gear reviews that mention sleeping bags (summer or winter) it's frustrating to note that others are carrying less in summer than me and not much more in winter than I'd take in summer. I've recently switched from a double- to a single-skin shelter, which is definitely draughtier.
My mat is an XS Thermarest Prolite, with my pack under my feet and lower legs and sit mat under my knees. I ought to look into getting a mat with a higher R-value.
I plan to invest in a warmer Primaloft jacket for Spring/Autumn use anyway, so I will try that with my current bag. I'll test it out before heading too far from home to check whether it affect the lofting of my bag. My bag is rather narrow, but so am (30" waist) I so I'm not sure how it will work out. Definitely worth a try though.
I've also been planning to invest in some lightweight Primaloft trousers for wildlife watching, so I could add these to the setup as well. I think these would be warmer for the weight than thicker long johns, but perhaps not so versatile.
I do try to have a hot drink, usually hot chocolate, before going to sleep, mostly for rehydration, but I usually get up for at least one pee in the night, which undoes most of the warming effect!
I have thought about adding a quilt to my set up, but got round to acquiring one yet. Might be more versatile than a new sleeping bag, and hopefully cheaper.
One thing that no-one has mentioned yet is whether they carry separate clothes specifically for sleeping in case they arrive at camp wet, or at least damp, to the skin (this happened to me five camps in a row in the first week of September). How damp can clothing be before it adversely affects the insulation provided by the sleeping bag? Is a clean, dry base layer under damp-ish day clothes enough? Or should one plan for all layers becoming wet? What are your thought on separate sleeping clothes?
Again, all advice and experience shared will be gratefully received
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