120hz null correction

Best way to fix a null in this region at the listening position? It is an enclosed rectangular 5000cuft room. Bass traps? Tuned port of some kind? What is the general approach to troubleshoot this. Cant move listening position nor the main speakers. Even if a trap would work, what specific spot would it need to be placed?

I have 12 couches/ottomans in the room that are squares approx 4x4' each. I wonder if getting a bunch of OC703 or other insulation material and stuffing the couches full would be productive.

It certainly cant hurt i guess. 2 (4) are on the sides of the room on each side midpoint. one ottoman is on each of the back corners. the rest of the 6 are in the middle of the room where we actually sit.

I am imagining a fairly mild effect if any at all

Turn the ottoman's into resonators with perforations on the bottom?

Am I insane to consider these options...

There is room for a large rug in the room. Would any reasonable material under the rug help with any bass absorption? It is a large uncarpeted floor at this point.