It's been years since I've recommended a book to everyone I know, but this book is so perfect for those balancing creativity and business, which is almost everyone I know. Including you.
He's a successful cartoonist who worked for 10 years as an advertising copywriter. Read his story at http://gapingvoid.com/about/ (Warning: he swears.)
He really gets and speaks to that dark struggle that artists go through: wanting to quit your day job, selling out to get successful and having it fail, or having it succeed, or not-selling-out and having it fail, or having it succeed.
But this is not a self-help book! He's slightly cranky, very realistic, and can describe your situation exactly since he's been there himself, then say, “But here's what I've noticed...” - and give you an insight you'll find useful for your own career or art.
It's a short lean book. Perfect for those who rarely find the time to read a whole book.
See my notes at http://sivers.org/book/IgnoreEverybody and borrow it from your local library, buy it from your local store, or click the Amazon link on that page.
(I read it as an entrepreneur and former professional musician, but I'd love to hear your unique opinion on it, so after you've read it, please post a comment at http://sivers.org/ie when you have a minute.)