Look in stores instead. It's so hard to tell quality of that type of book online.
If he is the kind of kid who is cool with second hand, I'd suggest op-shops. I collect old books and my kids know the value (specialness!) of an old book. I see so many beautiful atlases in op-shops. They are not all shiny and plasticy, but beautiful and big with great illustrations. I actually bought one the other day just because I couldn't resist.
Otherwise, my DD, who is seven, has a Collins Pictorial that she loves, and an older Jacaranda school one that she also loves.
Are you ready for many, many conversations about far off places, and the population, and the land types, and the flags, and languages (or are you already having those?)? lol, it's great when they show an interest!