I’m not in Europe so I don’t have a whole lot of knowledge about the healthcare system or how to direct you unfortunately. In terms of books I like Devon Price’s Unmasking Autism (one of the best for describing the experience of adults on the spectrum) and for younger AFAB folks I like Spectrum Girls Survival guide. I have skimmed and liked Field Guide to Earthlings but haven’t read it completely.
Also it’s a small organization but Autism Learning Lab is building some nice resources and education. I still believe a full formal social developmental assessment is helpful, but it’s expensive and if you don’t find the right practitioner they can still miss the boat. I tend to advise people to ask a lot of questions about their clinician’s expertise and experience with autism. Learning subtle signs beforehand and asking if they are aware of the “pink flags” etc. described here could help.