If you floor is uneven you first should discover why uneven. Inspect your floor joists to ensure no damage is present to the floor joists. If you have old plank style flooring you can remove the flooring. This is often best move for several reasons. First over years water as probably gotten into the flooring. Rot appears on the tops of the floor joists just under the old planking. Also about 25 years ago what was called chip board [cheap plywood only wood particles glued together under a press to make a board] was installed. This chip board can not take water at all. As water leaks etc. happens over the years including mopping with lots of water, the water seeps into that chip board causing both the old tongue and groove floor planking originally installed and the chip board rots from teh inside out. I just did this repair in one of my rentals. I pulled up what was solid of the old chip board and then pulled up most of the 1" tongue and groove planking that used to be solidly nailed down. I pulled up with my bare hands. Found some rot damage on the tops of the floor joists. I scraped away the rot best I could, then allowed to dry. Then installed 3/4 boards along the entire length of the floor joists on the top of the floor joists and then installed 3/4" tongue and groove plywood. Sounds like a lot of work but I put about $300 into material and worked about 24 man hours by myself removing and installing from floor joists up to finished floor for a kitchen, bedroom, and bathroom. Then I opted to install vinyl flooring.
Once you have either installed 1/2" plywood over the old flooring to create a smooth flooring surface, but only if no rot damage present, or did as discribed above as I did you may then install carpet, vinyl, or wood veneer flooring
Wood veneer flooring today is commonly a thin wood installed in a tongue and groove interlocking manner using finish nails to nail each board to the subfloor you created. then once all is done use a layer of polyurethane mopped over the new flooring rubbed into the grooves well to seal the grooves so water can not penetrate. Once that sealing is done you have no water concerns harming the floor anymore than you would have for vinyl.
Just for giggles I included a picture of what can be hidden under you old flooring. I only had one soft spot under the carpet in the bedroom about 2" around. Found what you see in the following two pictures.
Hope this helps
Wg
