I rock a Snugpak softie Merlin with a
Gore-Tex bivy when I'm not carry a tent. The packability and compression are outstanding if you have limited space and weight. Definitely a lot of great ideas on this thread. A cold miserable night could make or break a trip. A good base is where it all starts. I would start researching sleeping pads first and then work your way up i.e., sleeping bag, ...