Ask HN: How to get started with a sustainable bootstrapped business of your own?

Experienced Software Engineer working in Big Tech since the past decade. I'm at a point in my life where I'm feeling pretty done with a daily 9-5 job especially because of the overwhelming demands and random priority changes that expect you work beyond scheduled hours.

I could do this in my 20s and before I had a family but I've realized that it has become increasingly hard for me lately to manage everything especially raising a family. I'd like to spend time daily with my kids and don't want to pull 40+ hour work weeks anymore.

I feel like a sustainable pace would be working 3-4 hours a day and building something. I love building things so that always excites me but I'm not so excited/challenged by the people aspect of a job where you are required to be influential across orgs especially in as a Senior engineer in BigTech.

Anyway, all of this is just context for what I've been thinking since long: to quit my BigTech job and build something of my own on the side that generates just enough income for me to sustain and help raise my family. I'm at a stage financially where I have some cushion but not enough to be fully FIRE'd so I will need some income to sustain mortgage + kids + lifestyle.

Where do I start? What ideas do I explore? If any of you did it, what was your experience like?