It's actually a word of its own now: "I'm a booklover", although it's also acceptable to say "I'm a book lover" "I'm a books lover" is incorrect, but you can say "I'm a lover of books"

Why not just say : I love books?

If you love reading and collecting books, you could also call yourself a "bibliophile". If you are a person who is always reading, you could call yourself a "bookworm".

I'm a book lover is correct..