I have an old pine planked floor. It was sanded and finished about 12 years ago and is now in desperate need of redoing with another form of flooring. There is no sub flooring. It is just the planks and the floor joists. I need to cover it with something. My thoughts were a vinyl self stick tile. My problem is it is sunk slightly in the middle. My finances are limited so need a decent, cost effective way of laying a sub floor. Not sure what can be done besides a plywood sub floor. It should have a sub floor, correct? My rooms are small, about 13' by 13'. House was built in 1927.

Thanks for any info.