You can purchase all 3 circle resistance bands in our B3 shop here.
As a guide, the light band is 10-15 pounds of resistance, medium is 20-25 pounds of resistance, and heavy is 25-55 pounds of resistance. The heavy band should only be added when you feel the medium band feels too easy, and it is only recommended for lower body movements.
For sizing - Select the XS/S size if you wear XS-M leggings, and the L/LX for size L or higher leggings.
Cleaning: Wash in cold water/gentle cycle and lay flat or hang to dry.