Your mattress should be set up on a flat, stable surface. Options include a traditional metal frame with a solid foundation (like the Leesa Foundation), a platform or slatted bed (with completely flat wooden slats), or an adjustable base.
You should not use a traditional box spring with coils/wires, wooden slats that are arched or spaced further than 4.5" apart, or metal bases/platforms with thin wires. Because these types of bases do not provide enough support for the mattress, your warranty will be voided.
If you are not ready to upgrade to a Leesa Foundation, Platform, or Adjustable Base, you may wish to add a solid board, like plywood, on top of your current base. This will keep you in compliance with the warranty.