Here is a variation of the single-row buttonhole technique:

• Start by bringing the yarn in front, then slip the first stitch, bring the yarn back, and slip the next stitch.
• Continue by lifting three stitches over: slip one stitch, slip the next stitch back, slip this over, and slip the next stitch over.
• To prevent distortion, add an extra loop by doing a cable cast-on, bring the yarn through, do an extra wrap, and lift it over to create a little loop of yarn on the first stitch.
• Continue putting on stitches (e.g., one, two, three, four) and turn to the other side of the work.

By adding this extra step, you can minimise distortion on the side of the buttonhole at the start. Give it a try if you notice your buttonhole is getting distorted.