Sashiko thread is made of cotton, is relatively thick and matte. Unlike embroidery floss, it is spun in such a way that the threads cannot be separated; it is used as is.
If you want a thinner thread, you can buy it here, but this thickness is the "traditional" one. The thread is from Olympus Japan, a company over 100 years old! They have a lot of experience, in other words :)
Sashiko thread is a little more "fluffy" than embroidery floss, and adheres nicely to the fabric you are sewing into, blending in over time as an integrated part of the material.
Instructions for sashiko will be coming to this website eventually, but it will take some time. Many have wanted sashiko supplies for a long time, so I am choosing to sell before I can help with instructions in Norwegian for those who want them.
Search for sashiko on YouTube, and you will find a lot of good help! There are also dedicated sashiko groups on Facebook, for example, and several handicraft guilds offer sashiko courses, so check a handicraft guild near you if you are interested! The book Mending Matters also covers some sewing inspired by Japanese handicraft techniques.
You can find needles and thimbles for sashiko here :)