The Best Foundations or Base for a Latex or All Foam Mattress

I purchased a king Flobeds vZone yesterday and am trying to figure out what I’m going to rest it on. My bed is a platform bed from Room and Board. It has steel slats that are spaced approximately 5 inches apart. Flobeds, like most latex mattress manufacturers, recommends slats 3 inches apart or less.

Interestingly, Room and Board sells a latex mattress but they claim that no foundation/bunkie board is necessary.

Regardless, Room and Board sells the following platform board, which I’m considering placing the mattress on: Platform Board - Modern Bedroom Furniture - Room & Board

This is 0.25 inches of polyurethane foam over 0.625 inches of particle board, and then wrapped in upholstery. I’m wondering if this would be sufficient.

Alternatively, I could either buy additional slats for the bed, or purchase Flobeds’ coir, although the platform board + coir route is more than I’m looking to spend.

Curious what you all would recommend, thanks.