Since becoming less religious this is something I find lacking and miss.
All religions start off tackling spirituality and morality. Sit and think about everything and you have Buddhism. Focus on relationships and virtues and you have Confucianism. Focus on second chances and forgiveness and you have Christianity. Focus on serving a single dominant God and you have Islam and Judaism.
You can and should explore all of these, at least on a surface level. There's a lot of good ideas out there and people have literally sat around their whole lives debating and refining these ideas. Ideas that are not good tend to get lost to time.
There's a popular painting, The Vinegar Tasters, which depicts three men tasting vinegar representing life. Buddha thinks it bitter. Confucius thinks it sour. Laozi thinks it sweet. As a pseudo-religious, you could be unattached enough to understand and appreciate the perspective of these men.
Why not do all of them, understand why all religions are what they are. Religions are developed over thousands of years. Cults usually revolve around a common mystical experience. Religions often successfully translate that experience into a book and replicate it hundreds of years later.
There are a million "self improvement" cults out there all of which are dangerous rabbit holes to fall down. If it's got a website, a newsletter, a charismatic leader, and a few million outspoken supporters that's probably a sign to steer clear.
In my opinion there's some practices that help:
Seek out and talk to people you respect. Better if you can do this face to face, in real life. Having respected mentors should not stop where parents and school teachers leave off. If you're really stuck socially at this (as so many young people are today), try paying someone like a therapist of coach to get you unstuck.
Read old books. Actual paper books from before 2000 at least. Build up a good knowledge of human psychology, philosophy, politics, the arts and classic literature. Philosophy of human values is a good place to start.
Especially when you consider that 21st century writing is pretty much text messages and AI..
Do we just not stuff to write about anymore? Have all the good theories been taken?
Philosophically, I'd say yes. We don't quite have the philosophical manpower to work on these much. We haven't even seen any new social or economic ideas, despite things like software coming in and wreaking havoc on Adam Smith. Everyone knows what Marxism is, yet nobody has read Marx.
The past was quite different. Before paper, books were memorized, fully. People had to travel to libraries. They met the people who owned the books and studied under the past owner, directly, without any cliffnotes to distort the meaning. Muslim scholars not only memorized the entire Quran, they'd memorize every thing done by the Prophet Muhammad as well and build on top of that.
I always recommend people read Al-Ghazali, because he had access to the entire depth of Islamic knowledge from the prophet's time, the neo Islamic stuff that was built to deal with situations not covered by those laws, and was also totally familiar with Greek philosophers enough.
Technically, we could do stuff like that but at further depth, but personally, I'd rather be debating the virtues of SQL vs NoSQL. I did have a teacher who went in really deep into the philosophy, and I end up with whole pages of notes each time, even from one hour sessions.
It's like brushing your teeth. I can tell you it's good. But how do I sell it to you? I sell you belief - scientism studies and whatnot.
That's what religion is. It's things that are good and true for you and everyone around you, a handful of wise men recognize this, but then how do they sell it to everyone? Through belief. Unfortunately, you have a problem believing, but that's ok, lots of moderns do. But you seem to realize that what's being sold is actually good for you. You've admitted as much by saying you feel like something's missing. So just skip the belief part for now and get back to what the belief is actually trying to sell you: the philosophies.
Rather than waste time visiting a bunch of new age-y islands, maybe just get back to the shores you initially departed from.
Eg. Meditations and stuff like Buddhism Without Beliefs and Buddhist Daily Reflections.
> The race is not always to the swift, nor the battle to the strong, but that's the way to bet! — not Ecclesiastes 9:11
* see also Abelard, Sic et Non, ca. 1120
Because what is the end game if not reaching ideal?
Fortunately to have this ideal in your space doesn’t force you to follow any specific dogma.
But i bet finding a branch that fits you best is an easier task than coming up from scratch on your own.
And much more fruitful than finding it among pseudo-atheistic dogmas.
Or if you would like suggestions: empathy, kindness, forbearance, and forgiveness.
Good luck.