Choose two large identical pillows for the sides and one small pillow for the center.

Get the right size toss pillows, change the covers seasonally (introduce your accent colors)

Agree - the yellow/white in those pillows just doesn’t work at all - with the sofa or the rug. How many curtains in navy - how “powerful” is the navy in the room? Where is the sofa in the room vs. the drapery panels? I think I would not do 3 pillows in a dark navy. A mix is needed, as in Beverly’s picture/diagram above. And the rug is the West Elm ocean blue? It will have its own hue when on the floor in your room, with your own specific lighting. Sounds like you have settled on the drapes (or already have them), rug, and sofa. Get the sofa, drapes, rug in the room first, and buy pillows after you can see how the drapes, sofa and rug all come together in your space.

None of the pillows you show in that photo.

Yes - a sea of pillows out there! Get ideas by searching on Houzz or Pinterest (probably better for shopping for pillow combinations - sorry Houzz!). Don’t limit yourself to what you can find in stores. If you do buy online, go for pillow covers, and buy your own inserts separately. Just realize that you may need the insert to be a size bigger than the cover. Zip covers are easier to return, easier to replace, easier to get cleaned.

IMO if you need to move pillows to sit sown you have too many. I need to see your space that is how you get help with accents here. IMO none of those pillows work at all. What you really need is to hang some art in your space and use colors from the art for accents. Right now all I see is a sea of blue and a bit boring for sure .Amazon or Etsy have tons of pillows and sometimes a trow is abteer choice than pillows but i need to see your space

Arianna Belle has a terrific website for pillow selection, including guides onhow to combine sizes https://ariannabelle.com

I adore these pillows and I dream of ordering one for myself🤍: https://www.mapico.com.ua/products/dychyna-pillow-half-wooly