1. Relatively easy to read

2. Full of humors and informal expressions, specifically those whose formal counterparts are awkward to use in conversations

Well, I've got one book that I think maybe it can help you to improve your english. It is called: "The Curious Incident of the Dog in the Night-time " written by Mark Haddon.

It's a mistery novel where a boy who suffers of autism tries to solve a murder. The vocabulary is easy, maybe very easy because it is written by the perspective of the autist boy, so he speaks clearly and with lists and short chapters. However, in my personal opinion, there is lot of new vocabulary to work with, and you can find expressions used now-a-days.

I wish I had helped you.

PS. Meanwhile, if you chose this book or another, it would be grateful if you can say me the title of the book you had chosen, because I'm interested in reading too and if you can tell me about another one, I would like it. Thanks!

I`m not sure how good your English is (your spelling is much better compare to spelling of some native speakers I know) but the first English written books I read were translations by non-native writers as I found these a lot easier to read and understand (e.g. P. Coelho, M. Kundera)

When my English got little better I started with native writers (P. Auster, J. Irving, I. McEwan) and I was really surprised how much I was able to understand.

Well, if your English is not an issue, then I would recommend the following:

Tom Robbins - Jitterbug perfume, Even Cowgirls Get the Blues, Villa Incognito..

IMO, this guy is a beast! He uses funky comparisons and each of his book is a great trip. Unfortunatelly, his English is sometimes too advanced for me so I usually follow the original version with the one written in my native language.

If you are looking for informal expressions, I think Generation X: Tales for an Accelerated Culture by Douglas Coupland would do the job. As the name predicts, it is a book about pop culture, postmodernism in everyday life so there is lots of interesting expressions + the explanations are provided as well.

IMO, a great source of informal expression are books about a specific subculture. I usually just pick a favorite thing (activity, era etc.) and then google it in a context with books (e.g. novels about surfing, Top 10 books about hippies etc.).

Hope this helps,

Pav