The 12" MacBooks don't really have this issue. If they get hot, they throttle the processor to cool it down. My wife has a 2016 model that she uses on the bed occasionally without issue. The only time I notice it even getting warm, if I use it, is during OS X updates. It did also get a little warm during the Time Machine restore when i set it up. Day to day use, it stays very cool. My wife's is the Silver 2016, m7, 8GB, 256GB model. She does Office Apps, Facebook, E-Mail and general web surfing with Safari and Chrome as well as using a VPN client with Remote Desktop for work access on it. No games or heavy graphics apps like Photoshop. With that program load, it stays very cool.
I have a new 2017 Gold i7, 16GB 12" MacBook on the way (delivers Wednesday!) and hope it will be the same heat wise.