Here are my quick tips:
1. Add more indoor plants into the equation
(w/ space-saving vase/pot that can be hanged)
2. Upgrade your furniture into a sleek, modern style.
3. Put on lighter wallpaper/paint and window shades
(The whiter, the better)
4. Increase indoor lighting
Add white/daylight tint bulbs (but mind the quantity because you don’t want to add a lot of heat)
5. Regulate your indoor temperature
Opening a single window is not enough, there should be a circulation–so opening a door or another window wouldn’t hurt. (Or you can leave the bathroom exhaust on as your last resort); Turn-off airconditioning from time to time because it is necessary to bring in fresh air inside. Crack open a window 10 minutes daily should suffice.
6. Improve air quality
Plants are good enough but adding air purifiers w/ ionizers is better but stay away from ozone generators because they’re not environment-friendly.
7. If these steps still don’t work, I think the best way for you is to decide if it’s time for you to purchase a new home. The pricier it gets, the least crowded it is for you. But it’ll definite be worth it in the long run.