For this project I used PETG and TPU. This model is designed for you to split this object according to your bed size. 

UPDATE: Removed bottom lip x1 and made the feet less of a black hole for glueing by updating Tray x1, Front feet x1 and Mid back feet x2

You will need only glue and the parts to make this. 

As parts how many you need to print is in the file name.

Beware of the small notches and corresponding teeth. You may need to orient the parts according to it.

If you desire to make a cushion, you may change the bottom and top layers to 0 for TPU files in the slicer which they work as cushioning and a spill guard.

Please upload your makes and give feedback so I can modify this model to your needs.

The width is 17.5cm it'll fit any square armrest with around those widths. You can scale it to fit your couch also.