The only visa type that makes sense for this is a uniform short-stay Schengen visa.
The Schengen area does not distinguish between "business" and "tourism" visas, so you don't need to worry about getting a wrong kind of visa. The application form does at one point ask you to describe the purpose of your visit among several options that include "business" and "tourism" among others, but that is not because it will lead to different kinds of visas being issued. It is just to give the examiner an overall idea of the kind of story you're telling with your application. The important thing is that it is clear from the totality of your application which kind of visit it is you're proposing; they're not going to refuse a visa because they think a single question should have been answered differently.
If the conference is related to your livelihood, it would make most sense to describe your purpose as business. Your supporting documentation should include a description of the conference, a link to its official website, and (unless it is bleedingly obvious) an explanation of why it is relevant for you.
You should also -- as always -- provide solid documentation for your economic and social situation in your home country, such that it is evident that you reasonably plan to return home and continue your freelance work. Unfortunately freelance work tend to be difficult to document due to being irregular income, but you'll just have to do the best you can and hope for the best.
