darker and then also repeat the color elsewhere throughout the room

HI -- Not either -- that fabric will not last I think . And also maybe do not get limited on a strong color . If you could get the same fabric and color as your sofa and have an ottoman style that you could have choices of slipcovers . That is a way to change up the colors and patterns for different color schemes . Also that same idea for your accent pillows using a basic pillow and pillow covers . You have a great sofa .... great choice !

Why an ottoman? You have a huge sofa. Is there not enough space to put your feet up?

How about a big leather tufted ottoman in a darker gray than the sofa? Or black.

I think lighter if you are determined to go blue. Mostly because I think the darker clashes with your carpeting more.