Heya mama,
I didn’t use a doula but I have heard many mums recommend the following
Dr Janelle or Ginny from Four Trimesters.
Deanna Kearns does a lot of waterbirth in NUH.
Another popular doula is doula Lorraine Sanghani
https://www.facebook.com/lorrainethedoula
https://m.facebook.com/laboroflovedoulasingapore/