We have mentioned Adrien Rovero before. He is a furniture designer who specialize in space saving furniture with multi-function.
This green sofa has can be pulled out, and double function as a guest bed for a couple.
When you need a few extra sleeping spots, you just pull out the frame.
You can extend the sofa to double length with a spring mechanism, and rearrange the pillows.
It doesn’t look super comfortable, but as a guest bed it should do just fine.
It’s a great idea to get inspired by.