Your substrate is fine. Sand is bad, but reptile carpet is fine.
as I said in my previous post, UTH's must have a thermostat to control them. To get a basic thermostat and a UTH it will cost around $60. If you do go with a UTH there are a few things to know.
Mainly UTH's do not change the air temperature in the tank so if the room that the tank is in gets below 75 degrees a heat lamp will be necessary as well.
Here are 2 good thermostats, don't bother with the junk sold in pet stores.
http://www.amazon.com/gp/aw/d/B000NZZG3S
http://spyderrobotics.com/