That room model is great! You did an awesome job, it’s really helpful for visualizing your space! As far as giving it a cohesive, serene look, I would start by trying to establish a color palette. White always comes to mind both as a good starting point, but also a calm and relaxing color to feature. If it’s possible to paint any of your furniture white (here’s a tutorial on repainting furniture, if it helps!), I would recommend that to get those pieces to look more cohesive. Adding a rug over your brown carpeting will be nice to cover that color up!