About original question: you can simply change your player (probably a class inherited from Node2D) z_index property.
About your commentary:I really can't see a better way to create your own tiles other than, well, create them. For any engine ("serious" or not, whatever it means, be it Godot, GM, RPG Maker, Unity, Unreal or anything else). Unless, of course, you want to use something ready (if you pay/steal from someone).
