What makes a good problem for a bootstrapped company to solve?

I recently joined YC's Future Founders Course, which I think was new last year. From there I ended up on the Kevin Hale talk, "How to Evaluate your Startup Idea". In that he talks about what investors at YC look for when they're evaluating the problem that you're trying to solve.

He says...

  - We like problems that are urgent
  - We like problems that are really expensive to solve  
  - We like problems that are mandatory  
  - We like problems that are frequent

In the "How to Get Startup Ideas" talk, Jared Friedman has some good tips where he suggests the "Idea Quality Score". With it, there are four questions you use to rate your idea. You rate each of the four questions between 1 and 10 and then average the values to get your score. The questions to ask yourself are...

  - How big is this idea?
  - How much expertise do the founders have in what they're doing?
  - How sure are you that you're solving a severe problem?
  - How important is your new insight into this problem?

Other signs you might have a good idea...

  - Your making something that you personally want to have
  - It has only recently become possible

I'd like to create a small company while I'm working and I'd like to bootstrap it myself. So, I'm focusing on growth but probably nowhere near the startup founders growth. I realize there's a chance that I have "Schlep Blindness" and I'm rejecting ideas that seem hard. But, really expensive problems are probably out, unless I've got a great idea on how to solve them on a shoe string budget. So, I'm discounting the expensive ideas for my small company.

With all that in mind, what do you think makes a good problem for a small bootstrapped company to solve?

References:

https://www.ycombinator.com/library/6e-how-to-evaluate-startup-ideas https://www.ycombinator.com/library/8g-how-to-get-startup-ideas