Rules question, making a stance

Does anyone out there know for a fact the exact ruling for making a stance on the Tee.

I come across Tee areas that are uneven far too frequently, when my back foot (right foot) is lower than my front foot this exaggerates my my shorter right leg and causes me problems keepingmy drive straight.

Question is, can i use any artificial aid such as a piece of astro turf to make the teeing area where i place my feet level, or less uneven?

nothin to do with leg length but also you do have the ruling that the tee area/box extends 2 club lengths back from the tee markers

i have on a few occasions used this ruling because of uneven tee areas