Solid Hardwood, Engineered and Laminate Flooring - No subfloor Under hardwood Floors,Causeing

I have purchased an old farmhouse that was moved to its present location and is on a pier and beam foundation.It has nice hardwood floors,but it has some gaps and i can see daylight between some of the boards.The house sits about 2.5' off the ground,after crawling under the house I realize there is not a subfloor! This makes the house very drafty and hard to heat. Has anyone else incountered this problem and any ideas to elevate it? I live in a very humid climate.Thanks for any feedback! Ging

First, you will need at least a 6 mil poly to cover the entire soil surface under the structure, to keep ground soil moisture vapor from cupping the floor now, and to keep the crawl space in check, so the lumber from the underneath side can dry a little, before proceeding.

Bat insulation between the floor joistAnd then seal the underside of the joist with no less then 6-mil poly.