I've an area in our house where there is a large deflection along a wall (in the nursery). It's about a 5/8" deflection over 36" from the wall and angles down towards the wall. We are down to the subfloor right now and will be putting down refinished douglas fir. The door to the room is also within this deflection. On the other side of the door is more subfloor where we will be refinishing douglas fir and this too deflects down to the door. So basically I need to level the flooring 36" from the door on both sides of the door and also along the 16" wall in the nursery. Would it be better to remove the tongue and groove subfloor, shim the joists, and refit the tongue and groove subfloor (or put down new ply) or would it be better to put some #30 saturated felt down over the existing subfloor and use some self-leveling compound? I know it would be much more expensive to do the latter but I want to know what is best and most feasible.

As a latter thought, would it be better to sister the joist instead of shim it and raise the sistered 2x6 up the amount needed?