For some simple, affordable experimentation, you can try some round metal doorstops that can be found on Amazon. I have used them with success on speakers and on components. There are several different sizes/weights, and they only run about $10-$15 each.
https://www.amazon.com/Stainless-Stopper-Premium-SofiHome-Durability/dp/B01MFEC211/ref=pd_bxgy_img_3...
https://www.amazon.com/Stainless-Stopper-Premium-SofiHome-Durability/dp/B01MFEC211/ref=pd_bxgy_img_3...