I hope it's not a fools errand, as I'm currently attempting to do just this. I have a SaaS product that currently profits about £400/ month, and I have about £20k saved. I'm aiming to be living from my web app in 9 months.
If you're interested I'm doing a completely transparent blog series about my progress - https://blog.bugmuncher.com/2015/10/22/from-side-project-to-... and https://blog.bugmuncher.com/2015/10/22/from-side-project-to-...