Please help me figure out how to monetize my newsletter

Hi people!

I'm working on IdeaBot, it's a free newsletter and I'm thinking about turning it into a freemium newsletter.

(I'm not looking to get promoters, I'd like my newsletter ad-free for now)

The obvious monetization for me would be to double the daily ideas inside the reports for those that pay, but I don't know if it's "worthy enough".
Maybe add more benefits apart from this and charge $10-$20 a month?

I'd appreciate any comment on this!