The great outdoors

Hey Guys, I’ve been thinking about sleeping outside without a tent, just with a sleeping bag and a bivvy sack. Currently it is arround 0 to -5 degree C in my area. Honestly I haven’t read up on this much and it would be the first time doing something like that apart from some camping in the summer.

Is this a stupid idea? In my mind it’s fine as long as my sleeping bag supports low temperatures right? Or am I missing something big regarding safety? Appreciate your thoughts, tips and maybe sources to read up more about this!