My dad enjoys working from his chair, but if he did it for too long, he would develop neck and back pain. I purchased him a lap desk so he wouldn’t have to slump all the time, and the discomfort has gone away, but he can still work from his chair!
If your dad enjoys being productive while still being comfortable, I highly recommend lap desks as a Christmas gift. They even have ones that can hold a phone as well as a laptop, how great is that?