Sorry. I am having a little trouble visualizing the room. Is there a stone wall and another stone facade over a fireplace mantel? I guess it does not matter. But could you do a quick floorplan sketch and pass it on? If you want something computer generated, I use Sweet Home 3D
for simple floorplans. It is free, open source software and can be as accurate as you choose to measure. Works showing relationships just guessing too. Others on this site like Google Sketch Up
If you have not, you should set your monitor to 6500K which is the standardized color temperature for viewing and discussing color and it keeps everybody on the same starting page. It is especially important in sharing and considering neutrals like gray.
I see what you mean about lots of yellow! Yuck. In my work for clients I end up trusting a pixel grabber more than my own eye some times. But, the color balance on your photos looks off so I did not build you a color wheel or explore any charts. You seem savvy with color though so I will pass on the tool I use much of the time. I believe Color Impact
from Tiger Color
out of Oslo still comes with a free trial and a license is $40-50 or something. It is a wonderful program.
Anyhow, I would probably start exploring by pixel grabbing a specific gray you already have from the mortar or some color in the stone. The program will let you do all kinds of things like custom hue anchored color wheels (still the best way to know your color scheme options?) blends, schemes, noise and saturation explorations, value changes, etc. Your choice of color for the opposing wall may hide in these explorations somewhere?
The next step I use is to convert RGB color codes I develop in Color Impact into paint color. EasyRGB
if memory serves me) is another great, free program. Type in the RGB color, pick a major paint collection, and the system will kick out the four nearest paint swatch names and numbers.
The last tool I use is a virtual painting program. I spec Benjamin Moore paints most so use theirs the most. Sherwin Williams and I suspect others have them too. It is free (if you want the machine and not online version you do have to download and install Adobe Air
but it is free) and you can either pick a library photo close to your situation or upload your own photo, spend a bit of time masking off different paint areas, and then you can paint away---perhaps using the paint chip information you got from EasyRGB.
Anyhow, see if these tools help with a wall color selection or two and with incorporating your red sofa.
You might also want to play around with custom fabric of your own design to introduce color that way. A trend here is custom large output graphics for walls and some of the people who were doing vinyl vehicle wrapping are doing some amazing things for interiors. Sort of like custom wallpaper I guess but with more artistic license than conventional pattern repeats. I am thinking something more abstract than a literal mural would free you to explore use of graphics on other than that major wall?
While I have certainly worked with lots of architects and interior designers as a client and with them as clients, the only aspect of design I practiced in latter years was color. Keep posting your progress and thinking and I will be happy to help you tweak things if you do not mind airing our ideas in this public forum. When you can get them, some better and more accurately color balanced photos would help.
And by the way, and I have been harping of late, but the trend in lighting seems to be toward daylight temperature bulbs 5,000K or above. You must also make sure they have color rendering indexes 90 and close to 100 if you can. You do not want eery looking green people like the old flourescent bulbs used to produce because they had such poor CRIs.
Looks like you found a lovely home by the way. You might want to update your profile with basic geographic information so we know where you are?