For anyone looking for a good wash and fold delivery service by the kg, I just used and can highly recommend Tumble
https://www.tumble.sg/
They seem to be somewhat new, but replied to a question within a few minutes on WhatsApp. Book the service via website or app, and they happily picked up and dropped off with the hotel concierge (@ Conrad).
Turnaround time in about 24h as promised (basically same delivery window the next day. We left our stuff with the concierge around 530p. Pickup about 8p (you can track everything via app), and clothes were back in our room by 830p the next day. Combo of hotel reception + Tumble service made everything very easy. 50 SGD per sack up to 18kg.
Also this was all on the weekend - Saturday into Sunday. So even more pleased they could do the quick turnaround when most other places were closed or requiring an extra day or two.