Plywood for floor problem

[Jack]

I am replacing part of my kitchen floor, then putting a second layer of OSB over entire thing to get ready for some new hardwood flooring.

My problem is that I can not find plywood that is the exact same thickness as the plywood I am replacing. I took a chunk to Home Depot and felt it next to all the thicknesses available, and the closest ones were either 1/16 to 1/8' too thick or small. From what I have read it is crucial that the the floor is flat and level, so I want to good match. I did find OSB that is the same width, but I don't think that is strong enough to be the base floor (seems to work great as a second layer over the primary plywood. )

Any hints?

[EXT]

Either use the closest plywood possible and use floor leveller to taper the difference until it is not noticeable. OR use the next thinnest plywood and add some thin material to the top of the joists to bring it up to the level of your old plywood.

I would NOT use OSB as a underlay as it has poor nail holding characteristics and the surface makes for poor gluing nor bonding of ceramic tile. You would be better to use another layer of real plywood added to the top of your patched old plywood subfloor. My preference is to use flooring glue to bond the new ply to the old and add nails or staples every 4", with longer ones over the joists while the glue is still wet. You would be amazed at how solid and firm this method will make your floor.