I asked myself what was important in life over a decade ago, what is both fulfilling and pleasant (the former without the latter is not viable, the latter without the former is pure, empty hedonism, which wasn't an answer for me but it might be for the more beast-like among us) and my answer has been pretty much the same ever since: each other. Making meaningful connections with other people, the deepest and most unique ones being the ones made with your partner and children.

So, if you don't really believe in anything besides the "certainty" there's nothing after death and God has no plans for us after our short time here (or doesn't exist at all), I think you should focus on the practical aspect of life and just enjoy your lovely interpersonal relationships. If you want to go through the philosophically pointless effort of trying to give your life a deeper sense/meaning without an objective determinant that precedes the universe and existence itself and created it all for real but unclear/unknowable reasons, you're more than welcome to try but you'll end up in absurdism or hedonistic nihilism, neither providing a sufficient alternative (Nietzsche recognised this in his society about a century and a half ago and things have only gone worse since then...).

Finally, remember Solomon (and "Solomonic" means "very wise" for a reason) and his "Ecclesiastes". Everything being meaningless has been known for a looooong time, with a prophet dedicating a whole book to it. And it ends simply in "fear God and keep his commandments". God gives our existence context and meaning, being a good slave of God gives us peace and happiness (keeping good relationships with your peers and being generous and helpful is a big chunk of being a good slave of God, ofc). And, without accepting the possibility of God, you can't even hypothetically leave the realm of the subjective. This might sound bizarre if you think faith is just something you can put on and take off like a t-shirt, or compartmentalize while you think and behave however you want when it feels convenient, but if you understand it as simply the background to one's ideology, the framework everything rests on (Godlessness being the other alternative), you can better comprehend how and why its effects can be so large.