Been in a very similar situation to the OP ; attempting to create a Fraim on the cheap.
The ball nut thing is a good starting place - it's cheap. Well , if you already have M6 nuts and some 3/8" ball bearings it is.
Gave an improved sound with one layer of glass , and even better with a second layer immediately on top of it with ballnut support again.Reminiscent of Mana
from yesteryear but nobody needs to know ... it's only experimental after all. Tried 6mm balls but not as good.
At this point I tried introducing brass compression blanking caps to hold the balls . It certainly sounded different, and it's always going to be system dependent whether you prefer it .
Lived with this arrangement for a while before substituting all the metal for ebony pyramids of similar height ; this gave the sound I'd wanted all along.
Another layer of glass and pyramid (making 3 in total ) improved things further and if I'd had more glass I would have kept going.
Perhaps I should mention that the only thing living atop this concoction is an elderly CD player , and if it wasn't so damned sensitive to what it's sitting on
then I wouldn't need to be faffing around like this in the first place.
Take your time, evaluate slowly , and maybe have fun !
Nicholas.