What I always do is file the grooves in the nut to lower the strings so that pressing the string at the first fret is the same distance as holding the string down at the first fret and then pressing the second fret.
Do you get what I mean? Nut to First = the same as First to Second. I'm talking about the vertical distance the string has to travel to reach the fret.
If you hold a string down at any fret, and then with the other hand press it down the next fret, you will see the travel distance is very minimal.
Make it so that it's that way from the nut to the first fret also. THEN adjust your bridge.
If your neck is straight or near-straight, you'll have fantastic low action. If your neck is not at least near-straight you'll get fret buzz and NOW you can adjust your truss rod to get rid of that.
I've done this for 40+ years to all my guitars, including a 12 string and to all my basses and every last one of them has fantastic action. Other musicians say they all play like a dream.
There's no need to spend $3000 for a bass to get good action.
In the end if you still have one or two buzzing frets, it just means they're high and you can have them leveled or level them yourself with a little emery paper. It's not rocket science, like a lot of people think. Just go slowly and gradually until the buzz is gone.
There you have it! The "big secret" is adjusting your string height at the nut.
Good luck! You're gonna love the results.
