Substrate for a Sav

Hello,

I just got a new baby savannah monitor about a month and a half ago. Right now, for the substrate I am using just that "EcoEarth" stuff because i had a few blocks that I had already bought that I use for my other lizards. Well, I am out now, and I really dont wanna spend the money on more of it since it isn't the cheapest substrate in the world. I hear many people use mulch, and i assume you get that at garden shops and can get a lot of it for cheap, correct?
So what exactly am I looking for when i buy a bag of mulch? lol, anything in particular? Thanks

i use steralized play sand for all my savannas and they are fine. i have a 4 month old to a 3 year old. there has been no impactations ( i also put there food in a dish so they dont eat the sand)sand also is more natural substrate for them and it retaines heat better.

I use plain old garden center cypress mulch with mine.

I use peatmoss from the Hardware store