Sinatra for the night

My boyfriend and I are flying into Lisbon Friday and staying for 6 nights. We have 5 nights booked in Chiado area. However we have not yet decided where to stay the day we arrive. I’m thinking about staying in sintra or cascais that night instead of Lisbon. Would it be difficult to get there from the airport? Also hotel reccs welcome! Willing to spend money on a nice place. Thanks