I am a side sleeper or prone sleeper. When I sleep on my back I suffer sleep apnea, so I avoid that position. That means no hammock for me. Not that I would have wanted that anyway, except in those damned cases where I can't find level ground.
I like the idea of a bivvy, but I have felt clammy in a tent, and bivvies are even worse, according to what I've researched before, and these sources:
Having chosen my tent based in part on how well it ventilates, I would only use a bivvy for backpacking through a desert. From the reddit link: “I recommend bivys to people camping in dry areas (deserts and dry mountains like the Sierras) and wouldn’t recommend them for camping in buggy or rainy areas or for sweaty people.”
For the bivvy, I would also want a mosquito net and some room to move within. But having a mosquito net is a lot like having the inner shell of a regular tent, and the fly of the tent correlates with the tarp you would use with a bivvy. You wouldn't have any weight savings.
While you wouldn't have to worry about mosquitoes in the desert, there may be a friendly neighborhood rattlesnake. You ultralight bivvy and down sleeping bag may not protect you when you roll over onto the rattlesnake that is snuggling up to you for warmth.
Let's snuggle with the critters! If your tarp does a good job of covering you, then you don't even need a bivvy. For a mosquito net, wear one of those mosquito net hats. Or coat your gear with permethrin, and wake up in a pile of dead mosquitoes in the morning.
All you need is the ground cloth, the sleeping pad, and your cozy sleeping bag. Your backpack won't know what to do with all that space. You could get snazzy with a bigger mosquito net, that weighs 320 grams.
One downside, is that the tarp-tent is not free standing. I've been on a mountain where I couldn't find anything to dig stakes into. You could maybe make due with tying guy lines to rocks, but your choices for setting up can be limited.
Sometimes you need to clear some brush in order to take advantage of level ground for your tent site. That brush is often filled with thorns. Some pruning shears would really be useful about then, but even ultralight pruning shears would be rather heavy. Instead, use a survival wire saw to cut through those vines. Thread the wire saw underneath them, then bring them together while also stepping on them to lower them to the ground. The saw will make quick work of them.
In case it is a thorny bush instead of some vines, try to dig it out from its roots, or use the saw to cut the base. You can make that saw into a bow-saw by finding a branch and bending it to the ends of the wire saw, although finding the right size bendable stick may be a challenge.
You select the sleeping bag and sleeping pad based on the expected forecast temperature. Hot tip: some apps allow you to input the exact location for the forecast, which takes into account the altitude. The ground cover to protect your tent can be made of Reflectex Insulation, which has a shiny side to keep you from losing radiative heat, and increases the R value of your sleeping pad. See https://www.quora.com/Will-a-reflective-surface-such-as-aluminum-foil-continue-to-reflect-radiation-if-a-blanket-is-placed-over-it.
If you heat a large stone by placing near the campfire, you can clean it off and bring it in the tent when you turn in for the night. Place another stone over the fire's remaining embers, so if you wake up at night you will have another warm stone to fetch. Use your camping towel if the stone is too hot. If the stone is warm but not hot, you can place it at the foot of your sleeping bag.
Alternatively, you can use hand warmers and layer them between two pairs of socks for your feet. Fleece slippers or down booties also work well for this. The hand warmers will last all night.
Another option, is to cover the fire completely in sand or dirt, and then place the tent right on the fire pit.
If you gather enough firewood, you can keep a fire going all night. Pitch your tent close to the fire, but not too close where it could be affected by ashes. Use reflective mylar blankets, or a reflective tarp, to reflect radiative heat from the fire back to your sleeping spot. They can work well slid between your inner tent and rainfly. I'm going to be trying out the Adventure Medical survival blankets, a large size made for two person. Apparently they are made a little thicker and less tear-prone.
How close to the fire can you be?
So it looks like 10 feet is the going rate. However, traditional baker tents don't have modern ultra-thin 10D fabric, and won't get a hole just because of a little bitty spark. This guy has been making a modern version of a Baker Tent, and it get pretty toasty even in freezing weather:
When it looks like I'll be hiking in the rain, I'll bring along a mini umbrella. Yes, I'll have a poncho too, but I won't put it on unless I absolutely have to. It's humid enough without having to be covered in a layer of plastic. Zpacks makes an ultralight umbrella that weighs 6.8 oz (192g). Is that really lighter than other umbrellas?
You can also use an umbrella to catch rain if you are not near a water source.
Ponchos let you breathe better than rain jackets, especially if they also cover the backpack. A poncho can also function as a tarp.
The vestibule of my tent works for most things, but in situations where you want to enjoy a panoramic view outside of your tent fly, a tarp with grommets and some guy lines can provide an outdoor shelter. Bonus if the tarp is aluminized on one side (mylar). You can use the reflective side to heat or cool, depending on which way you turn it. Not only outside of your tent, but inside as well. Even without a fire, the tarp can reflect your own radiative heat back at you. With a fire, set the tarp between you and the fire for added warmth.
Reflective coatings are not durable, so heavy duty “emergency” blankets with tape on each corner provides reasonable sturdiness that can be replaced inexpensively when the coating starts to wear off. The following description from nsherry61 on WhiteBlaze.
1) Heatsheet (modifications were the ties-outs made with strips of 1 inch filament strapping tape. These were placed in a way to spread the stress up into the sheets instead of stressing just the edge. I didn't do any edge reinforcements. I just ran the corner tie-out tape strip about 10 inches, or so, up into the sheet material from the corner and the side tie-outs up about 6 inches in from the edge.
2) The other key to success was that all my guy lines had rubber bands on them as shock absorbers so the system gave nicely when hit with strong gusts of wind without overstressing the “fabric”.
To keep your gear dry, especially your sleeping bag, use a rain cover, backpack liner, and dry bag. Apparently, hard rain is very persistent.