I'm unsure that the Four Seasons will actually provide a roll away bed in the Cabana Studio - their website indicates that the only additional bed available in that room is a crib and that only Premier Oceanfront Rooms permit rollaways, likely because it's ~300 sq feet larger. Hotels in the US tend to take their occupancy permits seriously, because they're related to fire department occupancy approvals.

In Miami, I'm going to disagree with the thought that staying in a brand new FS hotel is the way to go. Service across the board is not up to par with luxury hotel service, especially on chains. I don't know what you're looking for on this trip, for the one night, but the hard product and the service at the Faena blow away everything out there now. The public areas are spectacular, and worth heading over to check out even if you don't stay there.