Instead of trying to get a PhD and a job in academia (which is very costly and due to "publish or perish" forces you to work on topics that are currently popular in academia), get a job that leaves you with a lot of free time, or find a way to retire early.

On the bright side, if we forget the "job in academia" part and just focus on the "PhD" part, a PhD can fit these criteria reasonably well.

Before I justify that, I should acknowledge the many articles arguing, with some justice, that a PhD will ruin your life. These articles make fair points, although I notice they have a lot of overlap, mostly concluding that if you get a PhD you'll spend 6+ years running up masses of debt, with massive teaching loads and no health insurance, worked to death by an ogre as you try to spin literary criticism out of novels analyzed to death decades ago.

The obvious solution: don't do a PhD in a country where taking 7 years to finish is normal; don't do a PhD unless someone's paying you to do it; don't do a PhD in a department that assigns you endless teaching duties; don't do a PhD in a country without a universal healthcare system; don't choose a supervisor who exploits their students; and don't get a literature PhD.

A "don't" is less useful than a "do", so here are some possible "do"s I'd suggest as alternatives:

• find PhD programmes where the successful students mostly finish within 4 years (in the UK, 3-4 years is a more typical PhD length than 6-7, but there is variation among universities)
• explicitly say on your PhD applications that you can't afford to do the PhD unless the university waives the tuition fee and offers a stipend (this no doubt reduces your chances of getting a PhD place, but if you're allergic to debts you want to be selective here)
• when you visit prospective departments, ask the professors and current PhD students how much teaching PhD students have to do (in some departments it's 100% optional, and pays you extra)
• do a PhD in the UK, which has a health system where most medical services are free at the point of delivery
• try to get an idea of how hard your potential PhD supervisors work their students (don't just talk to the supervisors themselves — try to talk to their current/former students one-on-one as well)
• get a PhD in physics, statistics, accountancy, economics, or something else remunerative and popular with employers

With the usual worries about PhDs out of the way, I turn to Wei_Dai's concerns. The first is the publish or perish issue. If you're just doing a PhD, the publish or perish imperative is often weaker than for postdocs & professors. (This again varies with the field and the institution. For example, as I understand things, top-tier US economics PhD students normally publish 3 or 4 serious papers, and basically staple them together for their dissertation. On the other hand, some UK physics students get PhDs without publishing any journal papers at all.) The ultimate hurdle for your work is convincing your supervisor and the handful of external examiners reading your dissertation that it's worthwhile.

Along the same lines, you don't necessarily have to work on fashionable topics if you're getting a PhD. It's quite possible to work on something boring; it need only be just interesting enough to keep your supervisor on board and satisfy your other examiners. (You'll probably want a margin of safety, though, in case your work ends up more boring than expected.) A more objective (but still approximate) rule of thumb: your PhD should be interesting enough to be accepted by the same rank of journal as the papers it's citing. If your PhD doesn't need to serve as a step up into an academic job, it can be as boring as you like as long as it meets the baseline.

Lastly, what about free time? A lot of PhDs eat virtually all of your attention, but some offer ample free time in the first couple of years if the work involved isn't fiddly. For example, you might end up running lots of simulations with a computer program that's already been written. If so, you might well be able to go to your office in the morning, set a run going, and spend the afternoon doing something else.

One catch is that it's not trivial to tell which PhDs are low-effort before the fact. Even if your supervisor accurately tells you what they expect from you, and the other students accurately report that they don't spend much time poring over their work, you might still get unlucky and end up slaving over a computer or an experiment or some equations for 16 hours a day, because research is unpredictable. (Still, compare it to the main alternative: people routinely underestimate how long they'll spend at the workplace — and commuting! — for normal jobs, too. It's not obvious that PhDs are more unpredictable in this regard.)

Nonetheless, if you plan ahead to do straightforward work for an easy-going supervisor who's not in the office most days, you might well be able to spend most days off campus yourself, doing your own independent research instead. And while you're a student, there's nothing stopping you from visiting other departments at your university to pick the brains over there!

Use your free time to search for important problems that are being neglected by academia. When you find one, pick off some of the low-hanging fruit in that area

I don't have any tips for this, though.