Mercerized cotton is the BEST yarn for cushions. That added sheen and protection means the stitches do not pile or fluff up as easily when the cushion is being used (more accurately abused) daily by kids and that cat. I made another cushion with cotton that turned out beautifully straight off the hook but piled so quickly it was really disappointing.
I used a beautiful cotton yarn from Weaving Yarn UK I got when I visited mid-Wales in the summer. This yarn is mercerized but still has an heirloom quality about it and is not stiff but soft and easy to work with: Valley Yarns Mercerized Cotton 5/2. They come in a quantity of colours as weavers use them too. This type of project would probably be a good one for weavers with small bits of yarn left because it only take a bit to make one square.
The pattern can be found online for free! It's called the Mitered Daisy Granny Squares pattern.
There is a free video on how to make the Daisy in the corner granny squares. After that I joined the squares together, before finishing with a scallop edging.
The video tutorial is by Ophelia Talks but I believe the original pattern is by Creative Grandma.
With 16 squares this took some time and I had to block them to make sure they're the same size.
The finished tapestry was really nice and soft to the touch. In these shots you can see that lovely mercerized sheen.