When I got back into vinyl a few years ago, I similar problems with a VPI aluminum platter and did an all on assult on the issue. I grounded the cartridge to the phono preamp and grounded the platter to the 120VAC wall source but using ground cable made from 1/4in wide tin plated copper braid (source Amazon) within Titeflex housing (source Amazon), some crimped connectors and heat shrink and it looks and works as designed. The platter needed to be grounded all the way back to the 120VAC wall source, grounding anywhere else did not work, and the resistance from platter to wall is less than 1.5 ohms. The best mat I found was a piece of leather remnant from a craft store that was very thin, about 1mm. Used a precut mat for a template, and use skin side down, suede side up, the suede side is very dense that couples very close to record. A similar leather maybe available from Amazon. For cleaning I use an optical cleaner Leader Lense Cleaner that is safe for optical coatings that has a very small amount of an antistatic. If you review the material safety data sheet, this cleaner has a small amount of an alkaline to buffer the di water, otherwise, di water will go acidic from absorption of air/CO2. The butylcellusolve is weak water soluble hydrocarbon solvent for cleaning, and is common in many water based cleaners.