You might try what was used to good effect in the final iteration of the TNT turntables, that is, squash balls. At each corner a properly sized piece of wood with a central indent on top (such as you can make with a large counter-sink, a spade bit or a forstner) can hold the ball in place with the TT on top of it. Adding something heavy underneath can complete the base: a sandbox, a thick butcher block, a piece of granite or marble.
Turntable isolation
My last turntable was a VPI HW19 MK4 .... with the springs. It's isolation from footfalls was terrible on wood framed floor. Are the modern tables with sorbothane feet better at isolating?