The two subnautica games are pretty good vanilla but I always end up adding the "snap to" mod for building and of course a map! When I want to just do base building the mod that expands your inventory is invaluable too. Lets just build and hold the resources you need instead of having to go back and forth.
Valheim I honestly don't think I've played the vanilla version. Theres just so many good content mods and qol fixes that I can't imagine playing it without