I know exactly what you mean - I've taken years off work to do with my time as I please, and I find that only people who have completely broken out of the cycle for 2+ months can relate. My biggest advice to you is to start searching for a new job now, and when you get offers make it clear you're only available to work 3 days a week (or 4, or 2, whatever you want).

It will take time and hard work, and it will pay off for the rest of your life.