I would agree with Lora on the temp. My warm side is 85°.
The problem with heat rocks is an old one and may have been remedied by new technology. I still wouldn't use them as in most setups the cord offers a escape avenue. Under tank heaters on a thermostat offer security and a much better degree of safety.
ZooMed makes good UTH and Hydrofarm offers the most economical thermostat on the market.

Amazon.com: Zoo Med ReptiThermŽ Under Tank Heater, Small: Pet Supplies
Amazon.com : Hydrofarm MTPRTC Digital Thermostat For Heat Mats : Plant Germination Heating Mats : Patio, Lawn & Garden