I was told that demons appraciate a black hexagram, you could begin with one made from ordinary card and them if you like the system, move up to something different?
You don’t NEED a circle or triangle, but they can be helpful to assist your mind in entering a state where symbols affect reality, and some items (such as the Universal Circle) are powerful tools, “actors” in their own right in the enacting of magickal changes (evocation is a change to the natural order of things, changing reality to confiorm to will is also just such a change).