Start With The Light
Most rooms that feel unfinished are not missing furniture. They are missing light in the right place. A single ceiling fixture flattens everything under it, and no amount of styling below will fix what is happening above.
The change is usually one lamp. Put a warm, low source in a corner that has never had one and the whole room reorganises itself around it. Shadows come back. Depth comes back. The sofa suddenly looks like somewhere you would sit rather than somewhere you own.
If you try one thing this week, try this: turn off the overhead light and switch on a single lamp at eye level or lower. That is the room you have been trying to buy your way into.