I make my own staggered top- and bottom-slatted modules using poplar that I biscuit-join to get the right depth. The construction method can be applied to virtually any kind of wood you'd want to use. Here's how the process looks in stages:
Stacking five units high poses no stability issues (and that's on carpet here). The same applies to placing module stacks side-by-side.
Not fancy, but it's a method that gives me expansion and placement flexibility at relatively low cost.
Jim