Choosing the right sleeping bag is a complex issue and requires advice. I would proceed as follows:
The first thing I would think about is how warm the sleeping bag needs to be for what I plan to do, i.e. what temperatures do I expect while on the road.
So I can make a first decision whether I need a summer or winter sleeping bag, or maybe one for 3 seasons or even an extreme expedition sleeping bag.
Many manufacturers specify several temperature values (determined in the laboratory) for this purpose. For example, we often see there a comfort value, a kind of limit value and an extreme value. I would take a very close look at which values are specified under which conditions.
Then I would think about the material. Down or synthetic fiber has already been mentioned here. Down can keep very warm and has a comparatively small pack size. It also absorbs moisture and releases it again (good sleeping climate) , but if it gets wet, it may fail its good characteristics and the filling may clump. Then synthetic fiber is in demand, combined with a comparatively large pack size. By the way, there is also water-repellent coated down. With down I would look exactly where they come from and how they are obtained, keyword: animal welfare. Synthetic fiber sleeping bags are easy to care for and durable. They have advantages in moisture and the filling is sometimes even silicone coated, making it even more resistant to moisture absorption. They are often also cheaper than sleeping bags with down feather filling.
Next thing I would look at is the shape of a sleeping bag. We see blanket sleeping bags, mummy sleeping bags and a combination of both (look like an egg shape). Mummy sleeping bags have less empty space than the blanket sleeping bags, so they keep you warm better. But there is a little less freedom of movement. However, the head, arms, feet, ... should not be too close to the sleeping bag, as this can create cold bridges. The egg-shape combines both somehow. I would try what suits you better. Exactly the same applies to the right length: try it out, every body is different.
Yes and then there are many details: how are the cords to pull the hood, are there inside pockets, is there an insulating collar on the hood, is the zipper on the right or left and and and. In my opinion, the only thing that really helps is to look at it and try it out, because this is really very individual. And of course many special forms, like sleeping bags that can be linked together, that can be used as a blanket, pure bivy bags etc.
This is a short summary from my experience and how I would do it. Especially if you are really dependent on a good sleeping bag, I would always get good advice before buying.
Ah, and if you were satisfied with your previous sleeping bag, why not take the same model again? I did the same, I had 10 years a winter sleeping bag from Ajungilak (the classic "Tyin Winter") and have been very happy with it. A synthetic sleeping bag. At some point the thermal performance was then no longer as good as in the beginning. From my point of view, 10 years and really many uses is also a long time. I just bought the same model again.
By the way, there is also an Overland Bound Boot Camp article that deals with this topic, check it out here:
Sleeping Warm in Camp Hello All, I am new to Overland Bound but have been travelling in the mountains for 29 years and spent over 10 years as a backpacking, mountain and raft guide. Being new here I wanted to be able to give back and contribute something to the group right off the bat. I...
www.overlandbound.com
Well, a good sleeping bag is important, because there is nothing like a good sleep on the road to enjoy the next day so right! In this sense enjoy overlanding!