I have recently found out that the translated and commercially available light novel has gone way past the anime material. I bought volumes 4, 6, 7, 8, 9, 10, 11, and preordered 12. I am now at volume 9 and I must say it is amazing. It is not written like a light novel at all, and the translator did a great job at using old English to better express the atmosphere of the story.
The anime covered volumes 1-3 and 5, so you can skip those, but if you liked the anime, the books are actually a lot better, so get them. The banter between Holo and Lawrence, the romantic developments, and the complex merchant plotting are all there, and going stronger than ever.
The art is also great. It is different from the generic art style used in the anime. There is a distinct warm touch to the pictures in the books. Look at the image, even Holo is inviting you to join the journey.
The series is already completed in Japanese at volume 16, but the English ones are continuously translated. Volume 12 will come out on August. It seems like 2 novels come out a year, so I am expecting it to be fully translated 2 years later.