For basic, relatively inexpensive, accommodations in the middle of the city, try the YWCA Fort Canning historic hotel on Orchard Rd near the Dhoby Ghaut MRT station. Roof top pool available. Convenient access via MRT to airport and major tourist sites.
Stayed there with the wife and 3 kiddos for a few days. Saw the sights. It was good enough as we were out and about most of the time.