I have a robens downlite from cotswold , very warm , but does leak feathers (Don't they all ?) Don't spend too much as feathers are a natural rottable material, i had a robens before too and the feathers by the head and in the footbag degraded until you could see the difference with the rest of the bag (condensation trapped at the feet and from my breath),so a cheaper (?!?!) one you can chuck and renew. If i could I'd opt for synthetic everytime , for reasons your well aware of. The temprature thing is ruled by humidity i.e. rain , and wind , just like your cooker , it can feel 10 to 20 degrees cooler , even if its above freezing, so plan for the worst, probably minus 25 at the outer limits !