You can do a lot better! I've used different things on top of my 4" thick granite machinists plate and the best by far is Townshend Pods. They look good too, and adjust beautifully for leveling.
https://www.audiogon.com/listings/lisa8492-townshend-audio-seismic-isolation-pods-set-of-4-sizes-a-b... Pods are sized according to the weight of your turntable. You can do the math or ask John Hannant at Townshend for his recommendation.
The main problem with granite is ringing. This imparts a hard edge to the sound. You may not notice or may even hear it as detail. Until it is gone, and then you realize how much better and even more detailed the sound becomes. I went through all of this with mine.
https://systems.audiogon.com/systems/8367 These are some old pictures I need to update them. Pods are now above the granite where you see BDR Cones and Round Things in the photo. BDR is very good but the Pods are quite a bit better.
If you can't afford Pods, Nobsound springs from Amazon are awfully good for the money. (I used them before upgrading to Pods.) You will have to play around with them to get the right number of springs, and shim or something to get the table level. They are nowhere near the league of Pods but way better than you would think for how cheap they are. The main drawback with Nobsound is the lack of damping. You will eliminate the ringing edge of granite and gain quite a bit of imaging depth and detail. But if you go to Pods they do all that too and better, with greatly improved (deeper, tighter) bass, and instrumental tone and timbre so much better it is like getting a whole new upgraded turntable.
