That's the exact substrate mix I started off with! My humidity is too high granted so I've switched to a bit more reptibark and less eco earth now which has helped me.
I heated the room a bit at first, but the big thing was adding the CHE plus the foam. The foam seriously really helps!
This is the foam I am talking about if you are not sure what kind I mean:
https://www.homedepot.ca/product/owe...dge/1000436411
Also holy cow. Yes stands are super expensive...
Does your thermostat have multiple outlets? I have my UTH and CHE both on the same thermostat, with my probe below my hot spot on the glass. That way neither of them are running 100% and they help balance eachother out.
One thing I should mention though is I got a very tiny 4W UTH and placed it on the side of my viv on my cold side. That raised the ambient temperature to the correct level for both sides for me.
Also, if you do not already have one, an infrared thermometer gun is SUPER helpful for this sort of thing, especially since you may need to put the thermostat at a 'higher' temperature to reach your desired temperature inside.