Here is a page from my double bass book, Ultimate Double Bass. This example is from the workout portion of the book. Here you will be going from 1/16 notes to 1/16 note triplets using various foot patterns.
It is very important to start slow and play each exercise for as long as you can. These are meant to be endurance exercises to improve control of your double bass. Let me know how they work for you. Have fun!
Ryan Carver is a professional musician and educator based in New Jersey, USA. Find him online here.