I did the same as you, and leafed through looking for Culture ships. I guess they're less prominent in popular culture and there are fewer images of them to use.
Banks usually describes the ships as oblong bubbles, and I've seen very few illustrations online that do service to Banks' descriptions. I like this one:
https://www.deviantart.com/ex-pacifist/art/Culture-GSV-and-e...
It's going to be a challenge to anyone who decides to adapt Banks into a movie or TV show.