Best heat solution for my snake? (Cold weather)

I’m taking care of a MBK.

The temperature in my house is around 15°C, so I bought a 24”L x 16”W x 14”H tub and a heat pad + thermostat for the heat side, which works under substrate (32°C). However, the temperature above substrate is around 26°C.
Substrate is 1-2cm aspen bedding.

That said, I have some problems with my setup:
- I need to maintain a mostly consistent temperature both below and above substrate.

- The cold side has a temperature almost the same as temperature in my house (15-20°C) so also I need to increase temperature on that side to at least 24°C.

What is the best solution for this case?
I was thinking about buying another heat pad + thermostat for the cold side set to 26°C (which is the max temp on the cold side for my snake) but I'm not sure if this will be enough to solve the problem above substrate on heat side (you know, because this could increase overall temperature inside the tub, so the "air" wouldn't be as cold to affect temps above substrate on the heat side).

If that's not the case, would I need to buy a ceramic heater + thermostat in addition to the two heat pads I mentioned earlier to increase overall/air temperature inside the tub? I think this might be too elaborate and an unnecessary expense, and there could be another solution.

I would really appreciate your help.

I've uploaded an image as a reference of my setup.

https://preview.redd.it/3d7enjxhv7ee1.jpg?width=1000&format=pjpg&auto=webp&s=9968c7d8d9033e1ac58d1453a28fd523055a6111