Get a job in SEO or start my own agency?

I’m currently working as a freelancer and I provide SEO and general content writing services.

My pay isn’t too bad but I’m ready to take things up a notch. So my question is, should I look for a formal role in SEO or should I build on my freelance work into an agency level offering?

My specialism is on-page SEO and I mostly write landing page and blog content. So my main worry with starting an agency is needing to also provide technical/off-page SEO.