Sewing machine needles by Schmetz are wellknown and of excellent quality.
With a twin needle you can make a seam in stretch fabric without loosing the stretch.
On the right side of the fabric you get the double stitchline and on the inside a zigzagstitch which makes the seam stretchy.

There are different width available, please choose the desired with when ordering.
The wider twin needles can have the issue that sometimes a little hill forms between the stitchlines. This is easily prevented by using Solufleece tape on the bottom and top of your hem. It's soluable in water. So just sew and rinse away
 

Is chossing difiicult?
In this PDF we have made a manual for choosing fabric in combination with thread and needles: (dutch)
Garen en naalden gebruikstabel

The manufacturer description: 
With the universal twin needle, you can turn clothing and accessories into beautifully eye-catching pieces: Use two top threads to sew two decorative seams at the same time. You can also quickly sew pintucks with the universal twin needle and a pintuck foot, without the laborious task of ironing pleats.
Thanks to the slightly rounded points, the universal twin needle can be used with a wide array of fabrics without any problems

TIP: a needle has a working lifespan of about 8 hours.

This does not mean you have to change your needles every day. It's like this: when you press the pedal of your machine down and hold it for eight hours straight. At the end of the 8 hours your needle needs to be replaced.

The easiest way of remembering to change your needles is to get a new one for every project.