What to offer?

I'll probably be offering an ebook written by me and another ebook also written by me plus some plr content and possibly a physical book and an audio recording of the book. I feel that's not enough to sell to the customers. What else could I offer to them? I'm thinking of proposing an addon to the base payment whereby then can ask me questions on a forum 24/7 and i'll answer them. How much should this cost on top of the base payment per month?