First I took a few measurements and made a pattern out of some light interfacing to get an idea of what to cut out. I got some foam from SL and cut the shape out using the interfacing as a pattern. I cut the foam in half across the spot where the seat bit meets the back rest so that once it was in the slipcover it would be easy to bend to fit the shape of the chair.
Then I wrapped some wadding around each piece a few times (just a thinnish wadding, nothing too thick) and secured it with some tacking stitches. I snipped bits of wadding here and there to fit it around the shape of the foam.
Once both pieces were wrapped I laid them down in between the fabric I selected (Amy Butler, Temple somethingorother, off Etsy) with right sides together and pinned around the foam shapes as close as I could get. Then I very carefully pulled the foam pieces out of the pinned fabric and stitched around the shape following the pins, leaving an end open for turning.
I ended up overlocking the edges after I trimmed the seam allowance back a bit to keep it neat.
Then it was just a matter of turning it right sides out and slipping the foam bits back in before slip stitching the opening closed.
The chair seems a bit happier and brighter now and I love looking at the colours on it!