Bad sleep ruins backpacking. A good sleep system isn't about spending a lot. It's about three pieces that work together.
The bag
Temperature rating is a guideline. Assume it's optimistic. A 20-degree bag will keep most sleepers comfortable down to 30. If you sleep cold, pick a 15-degree bag for a 30-degree night.
Down vs synthetic: down is lighter, compresses smaller, stays warm longer. Synthetic is cheaper, handles wet better. For the Southeast, down is usually the right call unless you're in persistent rain.
Mummy vs semi-rectangular: mummy is warmer for the weight. Semi-rectangular sleeps better for most people who move at night. I sleep in a semi-rectangular and I'm a light sleeper.
The pad
R-value matters more than thickness. R-value is insulation. You want 4 or higher for anything cold. Nemo Tensor and Therm-a-Rest NeoAir XLite are both great at R-4.5.
Closed-cell foam pads (Z-Lite) are bomber and cheap but bulky. Great as a backup or for summer.
Inflatable pads fail. I carry a repair patch every trip. Haven't needed it in a year, but I carry it.
The pillow
Not optional. Spend $30 on a Nemo Fillo or Sea to Summit Aeros and sleep like a person. Rolled-up clothes are a fine backup and a bad first choice.
How they work together
Your pad insulates the ground (which is freezing at night). Your bag traps body heat. Your pillow keeps your neck aligned so you don't wake up sore. If one of these three is weak, the whole system suffers.
Test your system in the backyard before a trip. Set it all up, sleep a night outside, see how you feel. It's the cheapest way to find out what's wrong before you're six miles from the car.
