Singapore has legal brothels, see link. You will also find some illegal ones in that are as well as hookers working the streets. You might also, as I did, just find some working in some of the touristy areas (I was just out to get some dinner and walking able to my hotel). The hotels may or may not look kindly on bringing them in the front door so if there are less obvious ways (say clubs and restaurants on a different floor) that might be best.

Used to visit every year for a few weeks around 10 years ago. Would go to Geylang and stick with the USD 50 girls. Once tried the $80 one and once $100? ones. Good bang for the buck at the USD 50 places. But no GFE or anything. I would give a $5-10 tip at the beginning of each session. One Thai girl gave me a BBBJ. But rest all CBJ except for the $100 one.