I found an interesting and comprehensive overview of entity options for NGOs in the EU (see PDF). Retrieved from http://www.a4id.org/wp-content/uploads/2017/02/EU-registration-options-for-UK-NGOs-post-Brexit-FINAL-PDF-1.pdf
EU-registration-options-for-UK-NGOs-post-Brexit-FINAL-PDF-1.pdf (1.6 MB)