One of the easiest ways to get a rare heart of the sea, prismarine, TNT and a bunch of other buried treasure is by way of the shipwreck at spawn in this Java Edition Heart of the Sea seed!
Island Flanked by Two Large Coral Reef Biomes
This Minecraft 1.13 Java Edition (or higher) Coral Reef Seed spawns you on a cool island that is flanked by large coral reefs. Lots of awesome Update Aquatic exploration to be had!