For those times where there's something specific you want with your sheets, here's how I made my own duvet cover and pillowcases, complete with soft linen and decorative ties. Below are stills and measurements to help you make your own duvet cover and pillowcase, along with a video tutorial. The pillowcase is essentially a mini version of the duvet, so I've just illustrated the duvet steps:

Every piece of fabric you cut from the roll should be "W" plus 6 cm, but how many of these identical pieces do you need? Take your measurement "L" and multiply that by 2, then add an additional 20 cm. Divide this number by "A" and round up to the nearest whole number. This is the number of identical pieces you need cut that are "W" plus 6 cm wide.

In my case 2*L+20 cm was just over 3, so I rounded up to 4. I then ordered 4 pieces that were "W" plus 6 cm wide. Once all 4 of these pieces were sewn together along the long edges, they formed one giant rectangle that could fit the entire duvet inside when folded in half.

When sewing, place the pieces right sides together and sew a straight stitch. Any excess length should be cut off and saved to make ties.

To sew the flaps at the opening, I folded the opening edges in twice and hemmed them with a straight stitch. Then I folded in the hemmed edge at 20 cm and sewed a straight stitch, creating a flap to hide the duvet cover.

To see how to make the pillowcase and ties, watch the video!