Slats are a great option but they do need to meet a specific set of standards. Slats should be the same width, flat and spaced equidistant from each other, no more than 3" apart.
Keep in mind that the Leesa and Hybrid mattress should be set up on a flat, rigid surface. Some slats are arched/curved/bowed or flexible, which will change the way a foam mattress is intended to feel and perform. Over time this can cause damage to the mattress and disruption to your sleep, so be sure to avoid those specific styles of slats.
Using those types of slats with your Leesa or Hybrid mattress will void our 10-year warranty.