I went to the thrift store this past weekend and they are having a sale on all sweaters, they were $1 each so I bought two. I suggest buying a sweater with buttons on it because it makes the project a bit easier as you wont need to do any overlapping for the cushion insert.
Measure the dimensions of the pillow and take those dimensions and draw them onto the wrong side of your sweater. Cut out the square, pin together, sew together, unbutton and turn right side out, stuff pillow, button up and you have a pillow.
Seriously, this took about 10 minutes. I think it's the perfect project for any beginner. And if it doesn't work out the investment in supplies is $1 or less.
Oh did I mention these are $40 at Pottery Barn?!