Can check out Hotel Fort Canning and Alkaff Mansion. I enquired both and went to look at the place....will recommend Hotel Fort Canning if you are looking for outdoor garden wedding, the lawn is very pretty and the price is cheaper.
Should try Hotel Fort Canning. i held mine at their garden terrace which is open air, best decision ever made!
Can look for Pui Wan, they have a wedding workshop coming up, can go check it out https://singaporebrides.com/temp/fortcanning-270713.php