My 1920 Craftsman 2 story home has 3" wide x 5/8" thick tongue and groove hardwood flooring strips/planks down as a subfloor...(grade level with another layer of hardwood oak? over it.) I had to cut it out along with joists that were rotted. now time to replace subfloor -Is my only option plywood??? should I be worried about maintaining the integrity/originality of home?