The cushions were 66cm so I cut two rectangles that were (66cm plus seam allowance) wide and ((2.5 * 66cm) plus seam allowance) long. Then I hemmed across the short sides (this was really fraying fabric, I should have overstitched everything before I started but I was too impatient!). They are simple envelope-backed cushions so I lay them on the floor with the right side up, folded the long sides at 33cm and then 99cm, basically you have a short end folded up and then the long end folded over that, with the seams showing. Then you sew up the sides and when you turn it the right way out - the short bit of the envelope is on the outside.
Dead simple but they match the curtains and they are lovely and soft - the fabric is plain sheeting too so nice and comfortable even in bed!