From an amateur enthusiast, not an expert:
This is a small room with the speakers placed relatively close to the front wall and the listener placed extremely close to the back wall. The location of the window actually helps a little, since bass tends to leak more easily through glass than drywall or concrete, so this transmission loss helps a little. The doors may help somewhat ameliorate the relative similarity of the length and width.
The two most important places to start here are behind the speakers and behind the couch. Because you want the broadest band absorption possible in these two locations in order to address as much of the frequency spectrum as possible, especially down into the lower frequencies, I would use no less than 3-4" thick absorption, and it would be better if you could use even thicker, as much as 6-8" if possible, directly behind the listening position. If you're making it yourself, you might consider layering two or three different densities of material, with the densest material closer to the wall, which might theoretically result in less reflection/refraction of higher frequencies by the denser material (think of the acoustical equivalent of Snell's law), but this is kind of a style point.
Once you've begun to address the front wall (adjacent boundary to the front speakers, will cause relative null around 150 Hz because sound will travel back, hit the front wall, and happen to arrive out of phase with the speaker at around this frequency, based on the measurements you gave, which will get more absorption from thicker absorption) and the rear wall (listener is very close, will experience too much relative bass boost because of adjacent boundary, plus too much reflected signal from an undesirable direction), then I would add a much thicker layer to the floor, preferably a cut pile carpet with an open backing, then a thick felt underlay beneath that. The cut pile will aid absorption compared to loop pile, and the underlay will extend absorption somewhat in the lower frequency spectrum.
If you're making absorption panels on stands, I would suggest making one or two to put in front of the television during serious listening sessions. Again, I would start with 3-4" if possible. These will be the most important places for absorption: behind and between the speakers, directly behind the listener. Too much 2" thick absorption runs the risk of resulting in a room that's "dead" in the mids and highs but boomy in the bass.
For making DIY bass panels straddling the corners, I would consider using denser material with a facing, like FRK 705. Here, the thickness of the panel is less important that getting more of the corner surfaces covered. The facing will change the absorption from purely resistive (depends on particle velocity, which is higher away from the boundary surface) to something more like damped resonance (depends on pressure fluctuations). I would actually try to use these to cover as much wall-wall corner and each wall-ceiling corner surface area as possible, making each product as wide up to 1 foot as tolerated. The reflectiveness of the facing may be slightly beneficial in keeping the room from getting too "dead"-sounding.
For the side walls, treating these may be somewhat optional, depending on whether you prefer more focussed localization (treat) or more pleasant spaciousness (don't necessarily need to treat). For this reason, I would put it lower on the priority list than the front and rear walls and the floor. I wouldn't leave the walls quite so bare, though. You could put up paintings or pictures hung at an angle to direct the reflection more into the floor (which you'd previously treated to be more absorbent) or taller bookshelves to diffract and somewhat diffuse the sound. If I were you, I would experiment here with the panels on stands that you'd previously made to cover the television to see what your individual preference is, since this can be extremely variable.
At this point, a ceiling "cloud" of absorption or lateral diffusion may be beneficial (or, with something like a curved BAD panel from RPG, a little of both), as might some diffusion elements located towards the sides of the rear wall to restore a little "life" into the room. You're simply too close to the rear wall for diffusion directly behind you, so absorption would be much better in that location.
I'd argue that small cushions in the corners of the room would probably produce less measurable improvement than the previous suggestions, although what you might perceive could be a different story. I'll leave it at that.
