i am renovating an 80 year old house and need some advice on the upstairs floors. the entire upstairs flooring is completly warped. the floor is t&g thus cannot be sabved and have a floor that won't make you dizzy when you walk on it. i know there could be numerous causes for this "slight" defect, however, i would love to know cause. of course that question could have any number of answers, lack of moisture, settleing, bad repair work, etc. the upstairs does appear to have been one large room in the past and where the walls were added some "mensa" candidate cut the wood flooring flush to the wall on the attic space sides.
my main quest is for any and all advice on leveling the floors. i am going to put down pine planks if possible.

thanks for any advice