Sony PS-6750 - mat suggestions
I have a TTS8000 which already has a damped platter. I replaced the original oil filled mat with an SDS isoplatmat.
It's an outstanding mat for lighter platters and the less existing damping you have, the greater will be its effectiveness. It retails new for about £90 but your deck is worth that investment. They occasionally come up used for around the £50 mark but you have to be quick.
A number of hardcore audiophiles and box swappers have bought one after "hearing" the effect of mine.
Main system: Sony TTS8000; AT1010; Audio Technica Art1; The Lentek; Cambridge 851n, Yamaha NS1000.
System 2 - SBT; Technics SH-X1000 DAC; Denon PMA-850