If you don't have a desktop it is likely your "office" exists wherever you happen to be feeling comfortable at the moment.
Unfortunately, that comfort usually comes to a screeching halt after about 30 minutes when it feels like you have a frying pan in your lap and your head is permanently fixed in a downward gaze.
What to do? You could take a folding plastic TV dinner table to the couch and work off that, or you can use an Offi overlap tray. A nice bentwood tray with room for your coffee and notepad or book, this gets your laptop off your legs and into a more ergonomic position. Not a bad option at all.
Available for $99 here