Some words about final steps and decoration.
I messed up one thing, so I would like to share this mistake with you if you ever try to do cardboard furniture. Before you do any impregnation (wooden glue and water, in the first step), you should have your piece of furniture completely fixed.
When I made side parts of the bed, I have impregnated them immediately before I fixed them to the inner construction. These parts, while they were becoming dry, have distorted a bit, which could be seen on the images if you take a better look.
This doesn't affect the stablity of the bed itself, it affects a bit of visual feeling. So I decided to use smashed newspaper as the final decoration, since it was practically impossible to tear it up from the middle construction. Just cover one side of the newspaper with wooden glue mixed with water and gently press it against the part you want to cover. Use your fingers to get a bit of relief.
Here is the detailed view:
Than I used beeswax all over the bed, and mixed a red color with a bit of black. With this mixture I colored the bed. When the color was dry, I took sand paper and gently removed the red color from some parts of the bed, so the black color came up again
Here is the detailed effect I have reached using this technique:
And at the end I covered the whole bed with varnish. Now I have to wait several days until everything dries completely. In the next days I will post a new image with final decoration of the bed.