I have used 3/8 with great results. The idea is to isolate the track from the table.
My current little layout uses 3/8 foam roadbed, track is put together with track clips.
Then two sided tape is attached to the clip and then to the roadbed. No mechanical
fastners (screws, nails etc) between track and table. Even the few trestles I have are
attached to the table with two sided tape.