My suggestion is actually not to find interesting clients. My suggestion is to find high-paying clients and then to become your own 'interesting' client (aka, reduce your lifestyle cost to a point in which you're able to use this money to sustain months of self-directed work).
Nothing is perfect and I've no idea whether this particular idiosyncrasy would suit other people - I'm still undecided whether it's for me.
I've been consulting with various clients for the last 4 years. I make a few multiples more than I need to survive, and do not work more than 50% of the working days per year.
This is relatively easy to achieve:
- I have no debt outside of a couple school loans, which I prioritize paying down to zero. Everything else is either living expenses, or discretionary spending.
- I ensure my clients pay for everything they need—hosting, Github, any and all services. This is an easy sell, as it keeps everything firmly in their control and they can replace me at any time.
- I charge by the day, not the hour. My clients have never complained, and they seem to find it easier to think and budget in per-day terms.
That's basically what I've been doing. I'm not convinced that's the only possible way, which is why I asked. Working on pointless projects is fine for a short period of time (at least for me - I tried that approach multiple times in the past), but a potential source of burnout in the long run...
Have you considered taking a pay cut to work more full time but at a company that you think is doing valuable work? There are a lot of companies trying to "change the world", surely one lines up with your values. Though sometimes the skills they want are more specialized than generic software development (which is what I have :( ).
Nothing is perfect and I've no idea whether this particular idiosyncrasy would suit other people - I'm still undecided whether it's for me.