This has been the dealbreaker for me whenever I've tried to bootstrap side-projects or incubate potential startup ideas while holding a full-time job. It always leads to frustration after a month or two, since I'm unable to perform to the best of my abilities on either the day job or the side project.
For me personally, the better route (for my sanity, at least) has been to double down on my career, putting everything into the day job. The big downside of course is that I've had to put any startup plans on hold indefinitely. But the upside is that I only have to focus on one thing (day-job performance), and since I'm lucky enough to be in an organization where performance is rewarded, that has led to career progression over time.
Rather than inflate my lifestyle, I've continued to live modestly and save/invest my compensation bumps. This extends my personal runway and increases my confidence that when the time is right, I'll be able to responsibly quit and focus 100% on my own thing without risking my family's financial wellbeing.
I know this isn't the right path for everyone, but for me at least it's what has kept me sane!