I also mostly read books (or consume media in general) in English and I was not raised speaking English. I had English in school but most of my English skills come from watching movies/TV shows in English with subtitles in my language. After a while I switched subtitles to English too.

It was not easy to take the plunge, first few books were definitely harder to read but I got used to it after a time - it also really helps your English to consume the media in it. I see it as easier alternative to go living in English speaking country - by far not on par, but was good enough for me (I'd not say I'm fluent though)