Hello KipMatthews,
Thanks for reaching Microsoft Community. We totally understand how important our safety when using the device.
As per Product safety warnings and instructions (microsoft.com), if your device is on your lap and gets uncomfortably warm, remove it from your lap and place it on a stable work surface. However, if you prefer to have a mat under your device then the better it is.
If this answers your question, please let our Community know by marking this post as an answer. This helps others who may have the same concern as you.
Kind regards,
StevenK