Early in the game the safest location to build your base is the Red Kelp biome which is locatedjust outside the Mushroom Forrest Biome in the direction on the mountain island.
This is a good area to build your first base because it is nice and flat and there is a wreck nearby that has plenty of fragments that can be used to construct Battery Chargers, the Mobile Vehicle Bay, and the Seamoth. It is also close to the Mushroom forest which is littered with Cyclops bridge and hull fragments as well as`lots of Lithium for base reinforcements and plenty of salt nodes for making water.