Thoughts please

[pseudonym]

There is Jerven bag, it is comparable in size to a sleeping bag, but waterproof. I got myself Extra and put in the car. I had an emergency this winter, took my family to the hospital and stayed in the car during the night - it was 4 degrees Celsius, but I felt very warm and this surprised me
Probably I will also get myself Jerven Original because it is compact enough to take for hunting. And it can be converted into a tent

Used to have one myself, great piece of kit worked well in -10c in Norway

[Zolner]

Great to see you're thinking this through so carefully. I lean the same way – individual gear provides more flexibility, especially if you ever need to split up. Bivvy bags + tarp are also much more discreet, and adaptable to different terrain if needed. The only downside I see is the limited space, especially on longer stops. But if you’ve tested your setup and it works for both of you, it sounds like a smart choice.