I spent some time last week camping in this shelter I built with my kids. It's roomy and nice, but not yet finished as I'd like to put some insulation on the roof for more rain protection. The bed however is finished and is like those above. Logs are lined up for me to lay across. It's the most uncomfortable thing imaginable to spend the night on as it is. I added 2 sleeping mats and 2 folded wool blankets over it and it was still uncomfortable- but I managed, and then complained the next 2 days about it. BUT, I was plenty warm because it takes 4" of compressed insulation just to block conduction in warm climates and this bed is raised, so convection is also an issue.
When it comes to battling conduction and convection, look at your arm. At wrist depth, you have enough insulation to get you through cool nights. Think cool summer, early fall, late spring. At elbow deep, you have enough for cold nights. Late fall, early winter and spring. That will work well to about 32 or so degrees. Armpit deep is what you need when the temperatures are below freezing. Remember to compress it and wallow around in it to make a nice nest.
The quality of a survival kit is determined by how much it can help you when you need to sleep. If you can sleep well at night, you have it made.” ~ Mors Kochanski
Gear
The right gear certainly makes a difference. We've already mentioned insulation layers, these are important is all sleep situations, including hammocks. The only time you would want to omit that would be at the hottest time of the year. Clothing you wear is important. Loose and layered to trap or release heat. The blanket vs sleeping bag dilemma usually comes next. The fact is that a queen size high quality wool blanket, like a 6 point Hudson's Bay Blanket, will permit you to sleep comfortably down to about 40 degrees. After that, you need more ground insulation, bigger fires or coal beds to make them work. But they can and do work below freezing. Sleeping bags are the way to go otherwise. Wiggy's brand are some of the best for the money and will keep you toasty warm.
Sleep Cycles
A quality nights rest in the woods takes time. If you exhaust yourself on your first night out it's one thing, but on a simple recreational trip, you'll find the first night is often the one you find yourself the most restless. This is because you're still set on your home sleep pattern. By your second night, you settle in better and begin moving back toward a normal biphasic sleep cycle. This may be new to you, but historically people slept in two phases through the night. One lasting about 4 hours when they would then wake for 1-3 hours and do things like read, snack, have sex or even chop wood! Then, they would sleep again 3-4 more hours until dawn. It was called first sleep and second sleep in pre-industrialized Europe. There's a book on the subject called "At Day's Close: Night in Times Past" by Roger Ekirch if you're interested in the history of night time escapades.
Nessmuk also references biphasic sleeping in his book Woodcraft in Chapter 3 on the Indian Camp.
"Ten o'clock comes. The time has not passed tediously. You are warm, dry and well-fed. Your old friends, the owls, come near the fire-light and salute you with their strange wild notes; a distant fox sets up for himself with his odd, barking cry and you turn in. Not ready to sleep just yet. But you drop off; and it is two bells in the morning watch when you waken with a sense of chill and darkness. The fire has burned low and snow is falling. The owls have left and a deep silence broods over the cold, still forest. You rouse the fire and, as the bright light shines to the furthest recesses of your forest den, get out the little pipe and reduce a bit of navy plug to its lowest denomination. The smoke curls lazily upward; the fire makes you warm and drowsy and again you lie down—to again awaken with a sense of chilliness—to find the fire burned low and daylight breaking. You have slept better than you would in your own room at home. You have slept in an "Indian camp."
It's normal to wake in the night in the woods, usually to pee. Speaking of which, never fight off the urge in the night to get up and pee, as doing so makes you colder as the blood in your body pumps around the bladder in an attempt to keep the water warm. This means your extremities get a lighter blood flow, which makes you cold. So get up and go. Stoke the fire. Eat a snack. Go back to bed.
Generally the first thing you hear around the morning camp fire is the question- "How did you sleep?" An answer other than good in the old days was often a sign of poor woodsmanship or a chronic condition, haha.
Proper insulation, good gear, and an understanding that it's okay to wake up at 2-3 am for a while- is all you really need to know to start getting a better night's rest in the wilds.