Just lay thermometer on the paper towel and let it sit for several minutes, i leave one in my tank and move it around to check the different area. It's glass encased, usually for a fish tank, and the 2 geckos i have like to rub on it, I often find either of them with their head resting on it as they sleep.
Warm to the touch is probably warm enough though. You have to consiter that the human body is about 97-98 degrees depending on the person. Room temperture where i live is about 70-75 degrees in someones house. So if i feels kinda warm it's probably just below 80 degrees, and you shoud also consiter that if you gecko, who is smaller then you, was to lay over it how warm would he be getting. You don't want it to be to hot if it's in his hide because they usually wanna sleep in there. They like to get a little warmer then normal after eating too.