Welcome to the easiest DIY project ever! Can you use scissors and tie knots at a kindergarden level? "Yes!" you say. Well then you've already mastered the skills needed for this project.
I used this tutorial from Simple Medicine. They suggest buying the 5/8 fold over elastic from Elastic by the Yard, which I did and I'd recommend that you do too. They have every shade you can imagine and my 10 yards of colors I'd chosen came within a matter of days.
Wanna take your newfound DIY skill to the next level? Measure out enough elastic to fit around your head and you've got yourself a super comfy headband perfect for keeping those pesky bangs out of your eyes while doing downward dog.