Choose one starting point
Take a colour from your rug, curtains or wall art. Use it as the link between your cushions. Two or three related colours can feel collected without becoming busy; cream, olive and a warm earth tone are an easy example.
Vary the texture
Combine a smoother fabric with a more textured surface. The difference catches the light and adds depth even when the colours are similar. Check the actual fibre and care label rather than judging maintenance from the photograph.
Consider proportion
Measure your sofa and the cushions you already use. A larger piece can support the corner, with a smaller cushion in front, but leave room to sit comfortably. A cover size and an insert size are separate specifications.
Keep everyday care practical
Rotate the cushions you use most and follow their labels. Do not assume a removable cover is machine washable. Address a spill promptly by blotting and using only a method suitable for that fabric.