I need help, well, my ball python needs help. On Sunday I bought my first snake, a baby ball python, when we came home I made his tank ready and then I discovered that the heat mat I used couldn't even bring the temperature up more than to 24 degrees. It covered about 1/3 of the tank so I guessed it was that the heat mat wasn't strong enough(only 7 watt). I ended up putting it in the tank underneath newspaper, and it got to 30 degrees at most.

So since on Sunday and Monday the shops are mostly closed, I went to buy a new heat mat, that was bigger (and this one is 20 watt, so I assume also stronger), today. We also bought different substrate that's supposed to be good at keeping humidity.

But now I've changed the heat mat and put it under the tank but again.. my tank doesn't get any warmer than 25 degrees! And as soon as I put the new substrate in (I used newspaper before), the tank started getting all foggy and the thermostat I have says the humidity is 99%! (Before it was changing between 50% - 70%).
The shop I was at was for reptiles, because I wanted to ask them for advise and they told me to get a heat lamp, but I can't get a heat lamp yet as the tank I have isn't that big (this will soon be changed to a proper terrarium), and I've also heard that a heat mat is best.

How do I make sure my snake is warm enough?? Why doesn't my heat mat work? I just want my snake to be comfortable but everything seems to keep going wrong..