Theraband is a brand I am very happy with. You get what you pay for. Yellow is very weak, followed by red, green, blue, and black.
My preference is to use the tubing for arls and bands for feet but you will get just as many different answers. Buy quality first then explore which works for you. I like to be sure I can move the body part through its entire range, and if it's too hard in the beginning then you won't strengthen the muscle (s) through its functional range. I don't think you can go wrong with the green theraband product given your youth