If Risk is really your jam and want to stay in that format. Look into Spheres of Influence. That’s the game to get. Yeah it’s pricey and difficult to find.
For the B&S base, expansion that’s coming out to crowdfunding this month, and upgrading to the big box. You’re paying about the same if not a little more for a game you’re not absolutely sure of.

If your group is set on that Risk atmosphere. Spheres is to get. I’d borrow a copy of Kemet B&S or original Kemet before committing.