1) To get to the sofa you have to get a bit creative with the wooden building blocks. Build a bridge or trampoline of sorts, see below picture for example.
2) The collider of the sofa seems a bit off judging from your screenshot, should also be an easy fix. thanks.
And yes... the checkpoints are, as of now, not saved from one game session to the next... this will of course be a must have as the development goes on!
A tip for now: keep the game session running in the background if you need a break and want to continue later... ;-)