Why do you want an index variable, what are you going to do with it? It helps to know the research question.

I suggest you follow https://stackoverflow.com/questions/54424440/create-index-based-on-categorical-variable

https://www.datacamp.com/community/tutorials/categorical-data

https://dapresy.freshdesk.com/support/solutions/articles/7000042907-how-to-create-an-index-variable-

Can be composite or the simple one....if different type of category in different items then simple one will be difficult....whatever you think you should think according to your objectives and study outcome.