For B2 self-study with a focus on Belgian Dutch, the best options are specialized textbooks from Flemish publishers like 'Nederlands in Actie' (which has a B2 level version) or 'Vanzelf Sprekend' (though it covers 0-B1, you can use its advanced sections as a supplement). However, most B2 materials are designed for Netherlands Dutch, so you will need to adapt by combining a solid grammar book with authentic Flemish resources. A practical approach is to use a general B2 textbook like 'Nederlands in Actie' (which is widely used in Flanders) and complement it with Flemish media, such as VRT news or podcasts like 'De Wereld van Sofie', to train your ear for pronunciation and vocabulary differences.
Honest tradeoffs: Belgian Dutch textbooks specifically for B2 are rare. 'Nederlands in Actie' is originally Dutch-oriented but has a Flemish edition with some adjustments; it is structured for classroom use, so self-study requires discipline. 'Zo Gezegd' you already find weak for self-study because it lacks answer keys and clear explanations. Grammar books like 'De Delftse Methode' or 'Nederlands voor Anderstaligen' are neutral but focus on standard Dutch. Your best bet is to use a textbook as a backbone (e.g., 'Nederlands in Actie' or the B2-level 'Taal Compleet' series, which is more self-study friendly) and then actively seek out Flemish input. For vocabulary, use 'De Standaard' or 'Het Laatste Nieuws' online, and for speaking practice, consider italki tutors from Belgium.
Concrete next steps: 1) Buy 'Nederlands in Actie' (B2) or 'Taal Compleet B2' (available online). 2) Download the free app 'VRT NWS' for daily news in Belgian Dutch. 3) Find a language exchange partner from Flanders via Tandem or HelloTalk. 4) Use Anki flashcards with Flemish audio from sources like 'Forvo'. Evaluate textbooks by checking if they include answer keys, audio files, and exercises for independent learners. Avoid books that assume a teacher is present. Remember: B2 is about fluency, so prioritize active use over passive reading.