I concur with a number of folks on here but my formula is a little different. I use IsoAcoustics Gaia footers under my speakers but instead of the carpet spikes, which are a pain to move the speakers around to tweak positioning, or a butcher block which I find raises the speaker height too much after combining with IsoAcoustics, I put the speakers with IsoAcoustics footers on 16x20x3/4” marble pastry boards from Sur La Table (I believe Amazon and World Market may have cheaper but perhaps lower quality alternatives). This adds additional mass while keeping it low profile, and offers additional decoupling with the use of the footers.
https://isoacoustics.com/home-audio-isolation-products/gaia-series/gaia-iii/
https://www.surlatable.com/white-marble-pastry-board-1634-x-2034/PRO-535591.html