Skip those small boxes they are tough to jump onto. I did a competition where they had those and the women did not like jumping on those. Too easy to tip over. Instead, I've seen some boxes get these for the 12" box jumps:
Non-slip surface and I believe they're stackable for easy storage. I don't know what long term durability is, but they are made to be walked on (not sure about thousands of box jumps but I'm guessing they'd hold up fine).
Hopefully your members will move up from the 12" box relatively quickly. I was training someone and she moved up to a 16" box pretty fast once she got over the mental part of it...
Get the 16x20x24 boxes. Much more stable and are common sizes used regularly.