To avoid that in retro sleeping bag from sticking him with sweat, use sleeping bags with synthetic lining, hydrophobic and technical underwear, that do not retain moisture in skin contact but they condense away from your body while avoiding the unpleasant sensation of wet. The techno fabric wicks and evaporates water away from the skin.
How to choose a vintage sleeping bag? Personal considerations, but supported by scientific studies published on the net and from experiences of friends backpackers like me: synthetic padding, internal and external, to avoid problems with water (stream or body), high quality backpackping sleeping bags with synthetic filling
at Pimasleepingbags.com, or very expensive, though Microloft or Hollowfiber 4 or Thinsulate cheaper but heavier, form a mummy to keep the lower internal space as possible and avoid air convection processes, and then cooling folding hood and padded, good padded tube inside the hinge (is a pipe full of insulation that protects the inside of the hinge as a seal, preventing the cold to pass), exact dimensions, not too tight nor too loose.
As for the temperature each must make his considerations depending on many, too many factors, so I would not give advice. Depends on where you go, what time of year, at that altitude, how long have you been prepared physically and psychologically … Arrange yourself
What brands? You should not talk about brands, but of materials and performance. You have to buy by reading the technical characteristics and composition, considering the different materials used, their quality, their insulation, compression, hydrophobia. You have to choose with great intelligence, not impulse. Within each there are different levels of quality brands. For example, the feather is of various qualities, and then by various services and prices.Within the same brand there are products that use high quality feathers and others who use quality feathers infima.
How to care for it? The feather is stored uncompressed, and outsmarted not rolled but at random, taking care to avoid moisture. Synthetic fiber does not require special attention. Should be followed though, for both washing and drying instructions. Low quality synthetic fibers lose insulating effectiveness with repeated washings, so it is advisable to use an internal removable sleeping bag, so you can wash the inside often, and lot less frequently. This is a Council that is also true with fibers that do not lose effectiveness with washes, such as Thinsulate 3 m’s, of course.
Attention: a good sleeping bag needs a good mattress, otherwise part of his estate go to hell. Here are some pointers in this regard: the mats.