If you want a table topper thinner, you could use dressmaking pellon. Pellon helps items keep their shape. It comes in different weights, and has a fusible option, so lots of choices there to get what you might be looking for.
A thinner top automatically loses the relief of the quilting and some insulating properties. I suppose it just depends on what look and use you are going for. From the comments, I see people are using table toppers for various reasons...
I made a placemat using an old piece of 100% polyester batting. I didn't like the thickness of it because it seemed like a plate was okay but a glass of milk seemed tippy and not stable. I used a really hot dry iron and fused the inner batting to itself and the result was a smooth flat placemat. I thought, "Wow, that worked out really neat!"