So, what you can do during your visit to Sri Lanka is spend one whole day in Colombo. Choose a luxury hotel in Colombo for your one-night accommodation, and you may also dine at a good restaurant in Colombo. Hotels such as Cinnamon Grand Colombo offer the best accommodation facilities, and they have the best restaurants too. So, yes... you can enjoy great rooms, food and even great nightlife from one place if you choose to opt for a good Colombo hotel.
Colombo attractions are located closer to each other. So, you may cover all of them within one day with ease. Choose tuk-tuks or even the public transportation network (buses) to get around in Colombo. Since app-based services such as Uber and Pick Me are widely available in Colombo, you may get their services as well. Driving in Colombo is something doable, but you will get fed up with the traffic jams and other chaos.