Using Soft Stackable Crossfit Boxes
Soft stackable Crossfit boxes are made from foam. Each box has a fixed height but they can be placed on top of each other to increase vertical displacement. Check whether you can secure these links for safety. Some will use Velcro straps while others may use clips or other mechanisms.
Look into their total weight capacity as well. Make sure that the boxes are designed to carry far more than your weight. Remember that jumps introduce greater force upon impact compared to simply stepping on a weighing scale. Ample breathing room is essential.
Despite being stackable, it would be best if you can work through the boxes starting with the lowest height until you reach the tallest one before using them in combination. Let your muscles get accustomed to the movements when the risk is fairly low and the challenge is easy. Form on improving your form and your landing techniques.