If human didn't invented bed, probably we are sleeping in a grass, cotton flower, leaves of the coconut tree that you need to tie them together to create human bed. And, also we can probably sleep in a mud. I grow up sleeping in a wood and not in soft bed. And human designs to survive with that, but because there are people who are very interested in creating such human bed , now we need to expense for such thing.
I also believe that human can survive without the commercial bed and wood, or just using plant leaves will make us feel comfort. It is so nice to too sleep in a grass but perhaps it is bot safe because of too many insects living in this world. And these insects will crawl you during the night while asleep. That is why we are very lucky that there is someone who invented bed to make us comfort to sleep at night.