Looking for suggestions for insulating an unheated room so the room above stays warmer.

With the exception of one room, the entire basement is completely finished as a separate living area. That one room is closed off from the finished area and has a door leading outside. The roof of this room is the floor of the upstairs sunroom. With no heat in the unfinished room, the sunroom above it is very cold. I'm looking for a suggestion to insulate the ceiling/floor. The sunroom does have heat, but with no heat below, it remains cold. The ceiling in the unheated basement room is corrugated steel, and the floor in the sunroom is concrete with vinyl flooring on it.

Would a layer of blown in foam insulation help? Or a drop ceiling with layers of insulation?

Any suggestions would be most appreciated.