[epistemic status: weak to very weak]
I see two different questions here:
One relating to the lack of "meaning" in your life, and one to related to the hedonic trademill.
As for the first, I don't know much about about crises in meaning, I've never had any. People have been saying good things about Man's Search for Meaning by Victor Frankl (LW review), but I haven't read it yet, so I personally can't vouch for it.
If you're simply looking to become happier, How to Be Happy is pretty much the go to resource here on the site. This won't grant you exit out of the hedonic treadmill, but it may shift the baseline upwards.
As for the hedonic treadmill: It seems extraordinarily difficult to exit it. Some possible approaches could include Wireheading (also, also, also), very high amounts of meditation, chronic pain and death. These are either very speculative, dangerous or undesirable (in the case of exiting the hedonic treadmill at the bottom).
Disclaimer: I'm not sure whether higher attainments in meditation could be classified as actually "exiting the hedonic treadmill". I think @romeostevensit has some higher attainments, maybe he or somebody else who is very experienced in meditation wants to chip in.
Not sure I can parse "on a hedonic treadmill w/ respect to education, career, significant other" properly. You keep getting better and better education, like people explain things to you more and more clearly, but you don't appreciate the improvement? Or just that you get smarter and smarter, but don't really feel better about it? No matter how high you climb on the corporate ladder, you feel bad about not being Elon Musk? Or is this perhaps about money, like no matter how much you make, there is never enough? Do you keep replacing partners with better and better ones, only to realize that all humans suck? Or is your long-term relationship improving, but after the big problems were solved, now you find yourself irritated with trivialities? Different options possibly require different strategies.
Generally speaking, the strategy for solving the situation of "having it too good, but not feeling satisfied" is to put it in near-mode contrast with having it worse. For example:
In some cases, the right thing to do is to change the game you are playing. If you have great relationship with your significant other, try having kids; this will reset your hedonic threadmill dramatically. Or perhaps stop seeing your career as an unending climb, but give yourself a specific goal, such as early retirement. Maybe you already learned too much, and it's time to start doing something else instead.
Possibly related: some people are maximisers, some are satisficers -- it means that some can't stop looking until they are sure they found the best choice, while for others anything that passes some threshold is acceptable. Generally speaking, the latter are usually much happier in life. Looking for the best option is forever stressful; you can never be 100% sure you found literally the best one; maybe a better one is waiting behind the corner if you only keep looking longer. And finding the best option doesn't even bring much subjective happiness, because if the best option is like 100 points of utility, and the second best is like 98 points of utility, the maximiser will feel like they only gained 2 points. And during the time you spent getting from 98 to 100 points at something, you probably neglected other aspects of your life, where greater improvement was possible. In the meanwhile, a satisficer was like "anything with 90 or more points is good", found the option with 98 points of utility and took it, and proceeded to improve other aspects of their life. Yeah, this is all oversimplifying, but the point is that being obsessed about getting the most can actually reduce your enjoyment of life.
What about other aspects of your life? Health, fame, spirituality, whatever. Maybe if your career and relationships are great, it would make more sense to focus on the remaining parts for a while.
Sorry, I shouldn't have assumed that hedonic treadmill is a well-defined/known term. When I say "hedonic treadmill w/ respect to education" I mean a scenario where I worked hard to go to a "top" undergraduate institution and thought I'd feel satisfied but don't end up feeling so. Then, I think that pursuing a "top" MBA will make me satisfied and I work hard towards that and the cycle repeats. Similarly for my career w/ respect to getting that next promotion, etc. The maximiser vs satsificer dichotomy does help as a mental model of how I might alter my mental calculus but unfortunately I think the hedonic treadmill applies quite broadly to my life and not just to a specific issue. Thus, it's a bit difficult for me to divert my attention elsewhere.
Thanks for the explanation and extra details! Here are some ideas:
Maybe the strategy "I will achieve X and then I will feel happy" is wrong in principle. Maybe happiness can only be achieved as a side effect of something you genuinely care about. Like, if you want to do X for X's sake, that can make you happy -- maybe not immediately, because in my experience the emotion felt right after accomplishing something is usually "I am so tired" -- but later, when you think "hey, X is done". However, if you don't really care about X and only do it because you believe it will make you happy, it probably won't. If you don't care about X, why should the thought "X is done" make you happy?
If that's the case, then you should expect that no achievement will make you happy. Which doesn't make them worthless, because they can still bring a lot of "okayness" into your life. Like, having enough food is better than starving, no doubt, but you can't eat yourself into happiness. Similarly, being rich is better than being poor; being educated better than being uneducated; etc. But also need something that makes you happy here and now -- either some hobby (that makes you happy by doing it, not because you expect some benefits in far future), or maybe something like loving-kindness meditation.
Or maybe you're just following the wrong goals. You do what the society in general, your parents, or your friends would approve of ("education, career, significant other" sounds like a generic template), instead of the idiosyncratic things you desire.
Or maybe you have a model where achieving X automatically brings you some outcome (something like: "if I get a top MBA, people will treat me with respect"), and it simply didn't turn out like that: you got MBA, but the average respect you get didn't increase; also, you keep getting higher in the corporate ladder, but you don't actually feel more powerful than before (you may get more power over other people, but the power someone else has over you does not decrease).
One possibility is that you are doing it wrong. Getting higher on the ladder doesn't give you more freedom; but working part-time or retiring early could. Still, getting higher on the ladder -- assuming it means greater income, and assuming you invest the extra income properly -- could bring you closer towards the freedom, so it is not bad in principle; it just won't happen automatically, you need to be strategic about it.
Also, emotions won't come automatically. If you want to get respect for having an MBA, you need to find an environment where people will respect you for having an MBA. The bad news is that it's not one of those places where everyone has an MBA; which is probably where you spend most time now. The good news is that 99.99% of population does not have an MBA, so maybe you just need to take a walk outside your bubble. (High-school reunion?)
Summary:
I've been on a hedonic treadmill my whole life w/ respect to education, career, significant other, etc. I've started to realize that this is unsustainable but also can't shake the feeling that I'm settling. Any tips and perspectives on how to deal with this?