Yeah, this rug is making a great contrast with your sofa! For measurements, I'd tape sizes down to see what fits best.

Looks good. I think I would size up. It will give you more space to stretch out or other furniture arrangements. You have a big room to handle it.

What is the flooring and have you selected the accent chairs? The problem when working with off-whites/ creams one can make the other look yellow. And photos often don't show the true color. Buy the sofa if you love it and then when you get it you can order the rug in the smallest size to get an idea if you like it in your space as smallest size is cheaper to return than a big one. And usually a smaller one you can find a home for it somewhere in the house or at the least use it as a sample for when you shop for other things.