Laptop comes from Lap, and Laptop were supposed to sit on your lap for you to work. The idea was to use the laptop for a short while and not the whole day.
People use the laptop all the time on their laps. With these laptop holder for lap you should not have a problem with your computer over heating.
Here is a selection of the best laptop holders for lap. I hope it suit your needs and you can work for hours in your couch.