Nancy Young wrote:

My question is this. What type of insulation would you
recommend? I was thinking some kind of spray. Is between
the joist batting, or that styrofoam product a better idea?

Any of the above would work. The spray is a good option technically, as
it also blocks air movement. Styrofoam is easy to work with. Around
here at least both are significantly more expensive than fiberglass or
mineral wool batts.

You didn't say where you live, but different areas have different
requirements for vapour barrier.

If you're going to be getting a building permit for the work then you
should be able to ask the building inspector what would be suitable.

Chris