A hot lap is a common problem for laptop workers (including myself - for more on the issue, see this strange warning).
So if you're tired of simply plonking a cushion on your thighs, why not test drive the CushTop which claims to provide "increased padded comfort when using your laptop on your couch, bed or floor. A convenient storage pocket keeps your power adapter and mouse tucked away. By flipping its platform over, the CushTop can accommodate small or large laptops." It comes in silver, orange or green and will set you back about £30.