Introduce some round chair cushions, to bring a different look to your room, to go with the usual square ones. These can be made to any size that you would like as varying the size can also alter the appearance.
Have a few larger cushions that you can sink into while watching television or reading a book for that extra comfort. Smaller cushions can be used as a headrest or squeezed into the little gaps that may occur at the side or back of your seat.
The definition of round according to the dictionary is "having a curved outline or surface, plump, cylindrical form and returning upon itself." to quote just a few.
This shape of cushion is well suited to be a scatter cushion and will compliment your lounge or bedroom. Bolsters are a type of rounded cushions but with a cylindrical, elongated shape.
These can be made into a deeper cushion with the addition of a gusset to form a soft chair seat or to be place on top of a stool.
This shape of cushions, with a gusset or welt, are perfect to use as an outdoor cushion pad for a picnic or sitting at a football, baseball game or anywhere that has a hard seat thus making these a little better.
Thinner rounded or squab cushions can be used for wooden kitchen chairs and are usually tied onto the chair backs with rouleau ties.
Wooden rocking chairs usually have a seat shape that suits a this shape, extra padding can be added for comfort.
If you are feel really brave then you could draw the circle straight onto the fabric using tailor chalk. But it is proabably best to trace around something to get a good pattern.
It is harder to put fastenings onto a circle shaped cushion as it is a bit tricky placing a zip into the seam. If one with a gusset was made then the zip would be in the middle of the gusset.
The best way to put in a fastening on this shape would be in the middle of the back. The pattern would have to be adapted to make the back in two pieces with the seam allowance allowed.