And oddly enough, there is only one kind of Gungan in FFG's Star Wars. Boss Nass must've just been an obese anomaly.

The Gungans in the book are obviously Otolla Gungans, one of the two major races of the species. Boss Nass was an Ankura Gungan. They might have rules for the Ankura eventually, or perhaps not since they've been so rarely seen in the films, TV shows, and other media, and according to Legends made up a very small percentage of Gungans.

I don't see why you couldn't use these stats for both populations of Gungans. The only difference I see is whether they have eyestalks or not. (I think the main reason Boss Nass' looks a bit different is because he is, well, fat.)

Star Wars Wikia claims that Boss Nass was a "typical" Ankura Gungan, so I wouldn't think he was enormous compared to others of his race. I'd possibly swap Athletics with something like Resilience to show that they are more tough and less agile than the Otolla but leave the rest as-is.

Grand moff Tarkin: "The Emperor has disbanded the senate. He has disbanded certain senators personally. With a lightsaber."

Ugh that is so corny. I literally can't imagine Peter Cushing saying that, in my head his voice turns into the voice of the bro who narrates movie trailers.