Underlayment for Pine "Hardwood" Flooring?

I’m planning to install yellow pine flooring over OSB plywood but I want to add another layer of plywood to make the floors more stable and even. I will be face nailing.

I’m reading I should add 1/2 inch CDX plywood, which I’m willing to do but are there any other options? other sizes of plywood? Also if I add the plywood underlayment, do I lay directly on top of the existing OSB plywood or stagger them for more stability?

Once I do that, I want to add rosin felt paper or plastic sheeting between the OSB floor and plywood underlayment. Necessary or unnecessary? This is directly over a basement.

Thanks, you guys are the best!!

I d recommend 1/2 ply wood and go perpendicular to the ply wood down now to get the most ridged sub floor.
Glue and screw this floor well,
Depending on the width of of pine flooring would determine what I d do next.
If you have anything wider the a 4" plank, I would both glue it down and top nail. Since your top nailing I m guessing it isn t tongue and groove pine. If you don t glue a wide plank , that isn t a T&G wood,when top nailing , you very likely to get cupping.
If it is a T&G wood your not as likely and use of a felt paper is recommended to help prevent wood on wood noise.
Any questions you can e mail me through my avatar. GL