So I am going on a 6 days wildness hike. I have a down sleep bag that can comfortably cover up to 3 degrees if I have thermos on. I am considering getting a sleeping bag liner. Main concerns are:

1. weight
2. volume
3. How many degrees this liner can increase in a sleeping bag

Can someone give some recommendations on how to select a small, ultralight sleep bag liner that can improve the the warmth in the sleeping bag as much as possible?

So I am going on a 6 days wildness hike. I have a down sleep bag that can comfortably cover up to 3 degrees if I have thermos on. I am considering getting a sleeping bag liner. Main concerns are:

1. Weight
2. Volume
3. How many degrees this liner can increase in a sleeping bag

Can someone give some recommendations on how to select a small, ultralight sleep bag liner that can improve the the warmth in the sleeping bag as much as possible?