A heat gun is handy for helping remove old floor tiles.
Sometimes one adds a new luan surface, quarter inch thick, screwing it down, sinking and filling where the screw heads are. Some use stainless steel staples instead of screws but the screws hold better. If the subfloor is still sound, filling in the voids with a leveling compound makes the best sense to me.
For leveling one could shim with shingles instead of using a leveling compound but the leveling compound is probably better. Of course there is the question of why the current floor isn't level. Are parts of it sinking because of rotting sills? My mother's floor is so unlevel that we gave up leveling; we'll eventually tear down the entire rotted kitchen wing and build anew on a concrete slab.