Singapore

We did a similar thing on the way to a recent trip in Thailand. We loved our stay at the Hotel Fullerton. It is a historic property right on the lagoon and you can see the drone and fireworks show from the rooftop bar at their sister hotel across the street. It also provides easy access to the major sights. It is expensive but they often offer value package deals (ours came with a voucher that could be used at the several restaurants and bars at the two hotels and the dim sum resturant was amazing!)

Can you share your budget in SGD so that we can make some recommendations? The Fullerton is indeed a lovely hotel, but there are lots of good options. Area wise, I normally recommend City Hall/Bugis as being a good central spot.

Without any budget guidance - for luxury, The Fullerton Bay (opposite The Fullerton), The Raffles (historic hotel in city hall), or the Mandarin Oriental (Marina Bay). Midrange range - the Swissotel The Stamford (city hall), or budget - Furama City Centre (Chiantown). But there are literally hundreds of options. The Furama is about SGD150 a night, ranging up to The Raffles at about SGD1,500 a night.

If you want to spend more time at the airport most airlines allow early checkin, either at the terminals or Jewel (up to 24hrs prior for some airlines), so you won't have to use paid luggage storage. Having said that I would normally arrive 2hrs prior. Boarding gates open 1hr prior and close 20 mins prior to departure.