Other thoughts for OP:

1) I think the best place to find what you're looking for is either YC's matching, or Indiehackers, or cold emailing people

2) Lifestyle businesses are fantastic! And there are many more people doing 7 figures in profit from software lifestyle businesses than people are aware of. (But also, a "measly 1M business" is really hard, and most businesses never get to 1mm/year annual profit)

3) It's very tough! Luck + relationships/access + skill + decades of practice/attempts. (Took me ~17 years of doing side projects before I had 2 businesses that worked)

4) Main skills needed: 1) Building things 2) Selling/distributing things

5) Focus on ideas where it'd be easiest for you to get the first customers. I'm also heavily biased to B2B, so focus on B2B areas where you personally know people who could be your first 5 customers.

6) > management consultants/MBAs who don't want to take the plunge and quit their regular jobs, but would be happy to do a few days a month to get a feel for startups

I'd suggest avoiding those as co-founders! Unless they can get you a first 5 customers. My sense is that most MBA skills aren't useful for getting a business off the ground, they're more useful for management consulting (which - what real value is that anyway).

7) Another option is to start small. Start yourself, build something for yourself. Do that as a side project. After a year, you'll probably have seen bigger problems in the course of building that side project. So at that point, switch and build a product that solves one of the problems you faced while building the first product. Repeat that for a couple years and you'll probably end up at some big $$ problems.

8) It takes a lot of reps to get good. I think the most underrated factor is how much time would you be willing to put into the thing you're working on. My suggestion is to sample many projects. Treat them all as side projects. Work on them for a few days (build product, chat casually with customers). Then ask yourself which one you most enjoy working on and where you could see yourself working on it for 6 weeks. Then work on that for 6 weeks, then scale up to 3 months, then 18 months. Takes time, so the one you'd most enjoy putting lots of hours into for weeks/months/years is probably the one most likely to succeed. And don't pick in the abstract / don't pick based on the idea, actually try working on them and pick based on how it feels to work on it - like taking a bite out of every dish at a restaurant - and then see which one you want to keep "eating".

9) Co-founders are great if a) you are capable enough to do something yourself and b) they bring something gamechanger you don't have c) they raise the ceiling for what the business is capable of. One of my businesses I did solo, the other with a 50-50 cofounder. Both worked out great, I think both paths are good. But the main takeaway from this point is to "be so good that you don't need them".

10) Pick something where you in your "sampling" you see that you enjoy the two critical pieces for that product/side project - building that product and reaching buyers for that product. The journey takes so so long that you have to be able to enjoy it.