I think the best single book about the end of the USSR is Stephen Kotkin's Armageddon Averted: The Soviet Collapse, 1970–2000 (Oxford: Oxford University Press, 2001, updated edition 2008). It's very informative without getting too long or academic, and it treats the collapse as more than just a single event. It covers really the entire period for decades on both sides as an extended epoch of instability, which I happen to prefer a little bit, historiographically speaking.

There's also David Remnick's Lenin's Tomb: The Last Days of the Soviet Empire (New York: Random House, 1993), which is more journalistic, less concise, and I haven't personally read, but it also has very positive reviews. I suppose, if you want a sweeping, broader, more up-to-date and historiographically useful but less immediate telling, I would go for Kotkin, but if you want something more exhaustive, narrowly focused, and human, I would go for Remnick.

Serhii Plokhy's The Last Empire: The Final Days of the Soviet Union (New York: Basic, 2015) is also well-reviewed, and Plokhy is trustworthy and brings an actual Eastern European perspective to the table, but I know even less about it and I don't really want to get that far out of my personal experience.

As for a biography of Gorbachev, William Taubman is generally quite trustworthy, and his Gorbachev: His Life And Times (New York and London: Norton, 2017) is pretty well reviewed, and I think it fits what you're looking for. "Unbiased" might be a bit kind to it, because Gorbachev casts such a massive shadow on present-day politics, but it's comprehensive, is the point. (I personally have a bone to pick with Taubman about the Moscow Metro, but as a biographer, he's highly esteemed.)