Ok tortoiseguru44, but sometimes it takes a little while for people to answer and if it is about a specific tort it will more than likely get the best answers if you post to that section. So I have moved your question to Sulcata Central. Also if you do a search for substrates that may give you the answers if they have already been posted.
First how big is your Sully?
If it is tiny a mix of 70 soil/30 sand would due nicely. Or you could use aspen or Timothy hay as your substrate.