Once upon the time I decided to make the bed for my newborn son. At first I bought the mattress in local baby store (the part I am unable to make myself). The mattress size is 40 x 90 cm. (All sizes will be given in centimeters, you can always divide them by 2.54 to convert them into inches).
Also I bought a sheet of birch plywood (10mm thick) and three round birch rods (3cm in diameter) in local hardware store. Pine rods are too soft for this construction, use hard kind of wood like oak or beech to replace birch if you unable to find it. I used three rake handles for this.
The construction is pretty straightforward. It consists of 2 flat panels and 3 horizontal wooden rods. This construction carries the cradle made from fabric with plywood bottom.
You can see my mockups in attached photo. I used the cardboard to do full-size prototype. You can see some amount of different shapes drawn on cardboard which I choosed from. Finally you will find the shape which you are fine with. Actually flat rectangular board will do the job well, but I wanted to have some pleasure seeing it. So it is "cloudy".