A few thoughts:
Are bugs an issue? If so, you will need protection. This could mean a tent, a bug bivy (just mesh) with a tarp, a weatherproof bivy, or some tarp/bugproof hybrid like the Henry Shires Tarptent products.
I like a tarp (which I do hold up with my bike, or attach to a tree, or use found sticks) because it is so lightweight, I do not have bug issues and I am not usually in a hurry (setup can be longer with a tarp as you decide the best setup for particular conditions). Tarps are very versatile- they can be set up in many configurations depending on needs (low and wind/rainproof, higher and airy/open, etc). My kit includes a tarp, a tyvek groundcloth and up to 12 stakes.
Tents can be a challenge because of dimensions and weight. Pole length is usually not that conducive to situating on the bike and they are generally on the heavier side. Those that have shorter pole sections and are super lightweight (Big Agnes Seedhouse or Fly Creek and other similar products) are quite pricey. In excess of $300 typically. Tents do give a more complete feeling of enclosure, though, which can translate to a better sleep. That is not something to be taken lightly.
Bivies are probably the lightest option for total weather protection as they use the least amount of material. But they can feel confining. I have only used one once and it was ok, but I wasn’t totally sold. I sleep on my side and curl up a bit and this was difficult in a staked bivy. If considering this, I would definitely choose a version that has a loop pole to hold material up away from your face. Outdoor Research has three models worth looking at – Alpine, Helium or Advanced. They make a very rugged product. If you can, get in one and see how it feels before purchasing.
Then there are combination options. The Henry Shires tarptents are awesome, but also pricey. But the combination of a tarp with netting for buggy conditions results in a super light shelter that is bombproof in pretty much all conditions. Worth looking into. If I were heady to a buggy place, I might get a bug bivy and use it with my tarp.
The last thing I will say is consider if you will be travelling alone or with someone else. A not too light 2-person tent might be perfectly light if you divide the weight among two riders. Similarly, a biyy only serves one, so if you are trying to get a friend or romantic partner interested in this, they will need a place to sleep, too. A tarp that can cover two people is a good option too. Mine does that and so if I go with my son, for example, all I need is an additional groundcloth.
I also wasn’t clear if you were asking about using a bivy instead of a sleeping bag. That really depends on your area and temperatures. I have a 45 degree down REI bag that packs super small for summer camping (got it at a Scratch and Dent sale for $50). But when temps are really high, I can get away with just a SOL Adventure bivy which is good to about 55F. And its REALLY small and light. Also waterproof and breathable. With my warm weather bag, it is warm to about 35F. It’s about $45. I also have a cold weather bag good to 20F for spring, fall and early winter.
Good luck! Part of the pleasure of bikepacking is figuring all of this stuff out and compiling the setup that best suits your particular need and proclivities. The two things I strive to protect myself from are bad weather (rain and wind) and cold (and I would add biting insects if we had them). If those are covered, a not-so-great pitch still won’t ruin your experience.
What he said.
I research the area I'm going to, then break it down to simple points to define my sleep system for the trip:
Weather type?
Temperatures?
Bugs?
Severity of the above?
Vegetation type?
Terrain type?
Luxury or fast and light?
Stealth or social?
Privacy or swinging in the breeze?
For the variety of trips that I do and enjoy, there is no perfect one sleep system for me, but I have an array of different modules that work for a custom situation.
Modules:
- OR Alpine bivvy, SOL emergency bivvy
- waterbloc sleeping bags, regular down bags, synthetic bags, mummy bags and hoodless bags
- silk and synthetic liners
- 1 and 2 man tarps (as tarps, groundsheets, groundsheet and cover - wrapped over like a bivy)
- 1 man groundsheet
- 1 and 2 man bug nets
- Tarptent Contrail
- Vaude Power Lizard
- short and long hammocks
- z-lite pads, synmats, downmats, self inflate thermarests
Knowing how this stuff works in given environments is key to putting together a near perfect system for each trip. Might be sleeping on snow and 40 below on one trip, and hangin in a hammock on a tropical beach on another.
Remember - good gear costs good money, so buy good gear to suit your purpose and it will serve you for many years.
I know this doesn't give you a direct answer, but I think it is an essential, logical foundation tool to learn and apply - not only for your sleep system, but also for other kit you need.
Give a man a fish, he'll eat for a day. Give a man a fishing rod, he'll eat for a lifetime...
