We also have it pretty easy now. Our youngest is almost 18 and he has a job that he's away from home for 20 or so hours a week.
When our kids were little, it was easier because there was 3 of them to keep each other company. We can't imagine just having one. Pop a video in and they were happy. We also were very stern (in our household, we are the boss, not them) that they be in bed at a certain time. We could have cared less if they didn't go to sleep until 3 in the morning, but they had to be in their rooms. Also, if our bedroom door was closed, they knew they'd have to knock, and we always gave them the same respect. We've never barged into their bedrooms without knocking. It was actually a very quiet household.
I think one thing that's really been beneficial to our kids is that we never hid that we were sexual people and that we needed alone time.