Good idea to buy a cooling mat. I'm not entirely sure what the temp should be while playing. However, you could search on a PC Temperature Monitor App or How to check your PC's CPU temperature.
I am not sure what to do to cool down the power brick. You might try placing it on a table with a fan in front of it to help keep it cooler. Don't touch the power brick while plugged in and the laptop is turned on.
If you need to move the power brick, turn off the laptop and unplug it. Let the power brick sit for awhile so it cools down to the touch. Then move it.
If you'd like to get a 2nd opinion or more information, please post about the issue over at AHQ Sims 4 Tech Help Board.
AHQ's Sims Tech Help Board:
https://answers.ea.com/t5/Technical-Issues-PC/bd-p/The-Sims-4Sign in with your EA account, click the New Topic button, up near the top of the board, to make a new post.