The other day my mom made me this beautifull bed. Looking on the internet for some ideas, she found this one. It was very easy to do. It only took a couple of hours and I helped her.
Here you have the sizes:

Place the two parts on each other and sew them along the edges. Remember that you must sew the fabric inside out. Leave a small part without sewing because you need to put the filling

Take the leftover fabric, cut 8 strips. These are the strings that will serve to connect each end of the little bed. Sew each strip as seen in the picture, it's basically a strip at each end of the sides of the bed.

Remember to leave some space to fill the bed with pillows

Finally tie the strips

This is how mine looks