Hi, stringreen,
I've found that the Herbie's Donut mats I use can actually sound better than a bare platter with thinner LPs because they reduce resonance vibrations (distortion) and especially because the mats maintain correct SRA when using micro-line and micro-ridge LOMC cartridges, which seem to be more sensitive to SRA. The heavyweight LPs are used without a mat.
Occasionally having to swap mats to accommodate different LP thicknesses takes all of 10 to 15 seconds of additional time. For me it's worth the effort. (Consider that most of my LPs are 1.0 to 1.1 mm thick and use the same mats so I don't change mats that often.)
Regards,
Tom