This might sound stupid, but what happens if you flip it over? Will it have a 0.1mm bump instead?

Also a tempered glass (the normal ones inside refrigerators at least) can hold max 30LB+, that is 13KG+ if you're afraid it won't hold.

Seeing as IKEA's UTRUSTA is also 6mm thickness, seems like it is an already suitable thickness.
As for changing it to 8mm, I think having a support at the bottom to prevent sagging and add additional strength seems to be better.

Good luck TS.