Most effective ways to measure SEO vs. Paid

Lots of companies with stagnating growth decide at some point to move SEO and Paid Acquisition under the same department to make them work in tandem rather than silos. If you happen to be a SEO specialist and get moved under a Head of Growth with a past career in either Paid or Product, you realize you now need some new ways of tracking and presenting your impact. What are the most effective methods or tools to measure SEO performance in a similar way to Paid channels?