A room can feel different without replacing everything in it. My starting point would be the way the space is used: where people sit, where the light falls, and what makes it easy to relax.
Make room before buying
Clear the surfaces, return things that belong elsewhere and take a photograph of the room. Notice the pieces you already like. Move a chair or a small table before ordering anything; a better arrangement may solve what first looked like a shopping problem.
Work with a small palette
Choose two or three colours that sit comfortably with the largest items you are keeping. Repeat them quietly through a cushion cover, a throw or a piece of art. The point is a sense of connection, not an exact match across every object.
Add texture with a purpose
A soft throw can make a reading chair more inviting, while a washable cover makes sense in a busy household. Check care instructions and measurements before buying. Avoid layering rugs or fabrics where they create a slipping or tripping problem.
Consider evening light
Look at the room at the time you actually use it. A reading seat needs useful light; a conversation area may suit something softer. Keep cables out of walking routes and use lamps according to their electrical ratings. Try one change at a time so you can tell what helped.
I would finish by living with the room for a week before adding anything else. A space that works for everyday life is more satisfying than a long list of new purchases.