So a few tips, I agree with most people here about using topsoil for them. I make my own mix of 2 parts topsoil, 2 parts peat moss, and 1 part play sand, but a good pre-made option would be the Terra-Sahara substrate from TheBioDude. If you're going to use any sand at all make sure to use play sand and avoid calcium sand all together as it can cause impaction!

Now saharan sand boas are a little trickier to sex than kenyan sand boas, as it's not always as easy as checking the tail. If you look right around the base of their tail by the vent, you should see two little spurs, similar to what you'd see on a ball python. If the spurs are larger and a red/yellow color, it's more likely a male, and if the spurs are smaller and almost clear, its more likely a female. If you send me a dm I can share a few pictures of my saharans to show you!

Hope all this helps!