I want my character to sleep ASAP from the start of the game. Where is the earliest place I can do that? Let's say it's in Riverwood. Is there or is it possible for a borrowable bed to spawn, like at a campsite, earlier than reaching Riverwood?
There are 2 places you can sleep before reaching Riverwood.
- A bed inside the Embershard mine (as stated by Rodrigo Guedes)
- A hunters camp at the first 3 ritual stones/standing stones.
Both will give you the "Rested" state.
Note that the beds inside the mine will require you to kill 3 bandits before being able to reach it.
Screenshots for locations: