OK, so let me say that I love being a self employed developer, and it is undoubtedly *good* money, it is far from "easy" money. There are a lot of things to take into account here, and a lot of different paths by which people become self employed developers. It's possible that the rare few have both light workload and plenty of money, but at least at first, finding legitimate high paying contract work is HARD.
Let me step back a few years. First off, I have about 20 years of experience in the IT field, and over a decade of that as a developer. I worked for most of that time as a regular W2 employee. This is my first point: Being paid well (or hired at all) as a developer requires credibility. You develop credibility over time, and there's no way to skip to the front of the queue. You command a high salary because you bring a breadth of experience that others lack, not just by virtue of the job title you put on your resume.
This also plays into my second point: You need to build relationships. At least at first, and probably for a long time thereafter, you will get your best work through professional relationships you have built by showing others what you can do, and being easy to work with. This, again, requires that you put in the time to build these things. Often, it will mean being flexible and willing to go the extra mile-- but people remember who was easy to work with and relentlessly optimistic just as much as they remember their credentials.
Third, enough work to make a real go of it takes time. Even with credibility, relationships, and the skill to back up your work, it still may take months or years of slogging at it before the pipeline starts to fill up. It'll be some small one off jobs here or there after six months of looking, or a half time thing balanced with your W2 job, or whatever, but it will very likely take time.
The summary of my thoughts above is that most people who want to be highly paid developers working on more or less their own terms need to first earn the right to do so. There are exceptions to every rule and I'm sure there are some people out there who fell into a viable self employed situation with little to no skill or effort. Generally speaking, though, you are a business owner and that means taking responsibility for busting your ass all day, every day, odd hours, on the customers terms, and usually as someone else's employee for a good while, before you can make a go of it by yourself. Alternately, this means innovating from the ground up on your own, which while certainly possible, is not where I've made my money and carries more inherent risk.
Don't take this as discouragement, though. I freaking love it. I recently got what a few years ago I would have considered an impossible-to-pass-up W2 offer, and had to negotiate the ability to work it as 1099 because I don't want to give up the tax and retirement benefits of self employed status. I don't have all the flexibility you mentioned; I live in a high COL area and pretty much have to stay here and make the occasional appearance in an office, but I'm also saving at a rate that a same-pay W2 developer couldn't hope to match due to tax benefits and retirement vehicles that only the self employed can... employ. I just think you're probably in for a few years of groundwork first.