Make sure you have classic world size, large biomes, and good biome mix ticked off.
mushroom island is in northeast, snowy biome, igloo, trees, and pumpkins in southeast.
Both shipwrecks peak out of the water. the first one is by the north side of the huge lake.
the second in in the middle-west of the ocean. the huge lake is in the mushroom fields.
Coral reef east of mushroom fields. Igloo in southeast has basement. sorry for no coords
To mine or not to mine, that is the question!