The tortle package is simple, but enjoyable. It fleshes out Chult to a good extent, and allows further exploration (assuming your players don't feel too rushed by the Death Curse). It has a single dungeon, some flavor spots that build on the overarching lore, and some exploration options.

The main draw for most people will be the Tortle race, but I feel this is the weakest part of this package, it's fun flavor-wise, but is not a wholly useful race (just my opinion).

If your players have fallen in love with the setting of Chult and have some Tier 1 wiggle room left, take a look at this supplement.