I use a Laptop for rendering. Sometimes nonstop for weeks. Heat is mostly between 80 and 85 Celsius.
This is with the manual controlled fan and with a laptop stand that does have another big fan in it underneath.
I made a test with the stand it makes only a difference maximum 3 Celsius and probably much less.
So don't count on them so much. It is better then nothing of course.
Heath is important but if you are so afraid you shouldn't use any machine that is heating while working.
Just search for a laptop that is good for this kind of work and stay away from laptops that get too warm.
My laptop is kind of a good one with 16 GB RAM , I7 CPU etc... But still i use the laptop only because of too long rendering hours.
It wasn't the first reason to buy. It was more a just in case i need it and for work when away from home.
I would always prefer a desktop computer for rendering and work. It is much more flexible from any point you look at it.
Except one point of course:portability. Working on a small screen with a small keyboard isn't nice.
I use TightVNC to work from my main desktop pc on my laptop even when they are side by side.