Finally!, I finished my mitered square cushions yesterday night. The knitting of the squares, which I made entrelac, was fun and easy, though it took me several months according to my Ravelry notes :)))
The inside cushions are also home-made - I could have bought ready made in the right dimensions, but where's the fun in that :)))
The cushions are 40 cm by 40 cm, a total of 25 squares each. I knitted a border of two rows of stockinette stitch in the color of the back side. Initially I planned to sew the border to the back side, but I actually liked them bordered, so I crocheted an additional row of single crochet (sc) as the real edge of the knitted square.
The back side is upholstery fabric, similar to the upholstery of our sofas.
The zipper is placed at the bottom of the cushion:
Probably it's beginner's luck - I had never before sewn knitting with my sewing machine and was quite worried. But the first cushion came out perfect from the first try. Encouraged, I thought the second would be easier and even tried some improvements. As a result it took me at least thrice the time and effort and the improvements proved to be for the worse. The moral: try to avoid making things in pairs!