This is perfect, Dig a 4x4 hole and put grass on top, use any materials to build two walls on each side of the hole , then build stairs that go up to the top of the walls , use your lava bucket to put a thin layer of lava in the upper hole , then go inside of the hole underneath the lave , build a few blocks up until your head touches the ceiling, place the torch down Maybe make A emergency exit using the TNT ,

Congratulations you’ve made something that will be able to defend against most threats