Insulation in floor

We live in an old 3-story house. The 3rd floor(attic) is semi-finished but not heated. I want to add insulation to the floor of the attic/ceiling of the 2nd floor, as we are losing a lot of heat from the 2nd floor bedrooms. I am not opposed to pulling up the floor boards to do this. We may eventually finish the 3rd floor and add heat but not in the near future. The 3rd floor is very hot in the summer and very cold in the winter. What kind of insulation should I use? What about a vapor barrier? Is there anything else I should be concerned with?
Thanks.
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I would use blown in cellulose which would not require the floor to be disturbed too much, For a vapor barrier I would paint the ceiling of the floor below with Insulaid or some other vapor barrier paint. It can be overcoated with regular paint afterward.
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