Reupholstering is supposed to be more expensive than buying a new sofa. since you put down a nice chunk of change for this one, I would consider contacting the manufacturer to see if they have someone who can repair the buttons.

Alternatively, someone in a dry cleaners probably knows how to sew on a button, so if you have a good relationship with your dry cleaners, you could ask them if they would be willing to do this.

Or maybe just get a seam ripper and remove all the buttons so it looks the same all over?

I have a gorgeous modern tufted sofa, but the buttons have all fallen off and the cushions have become untufted. I'd really like to get it reupholstered without tufting, am curious about how much that costs. Is it worth it, or should we just buy a new sofa? This one cost about $2000 four years ago.