You can muffle the sound using pretty much anything, packing cavities with insulation are the cheapest.

Keep in mind that all the walking noise, etc is transmitted through the joists themselves, so you need to isolate them from the ceiling planks to achieve the result you want. Here is an image to give you an idea only in your case it would be planks. If budget allows and you can put a layer of sound reduction sheetrock in addition to planks that will give you what you want.

Good luck

fill the gaps with foam, insulate with rockwool, and use resilient channels to attach to joists.