Oh dear, I really feel you on this, an unplanned complication is already so stressful, and you're still trying to think ahead for your own comfort, which is completely understandable.
From what I generally know, at KKH the subsidised route covers up to Class B2, and B2 wards are actually non-air-conditioned shared rooms, so if you want air-conditioning (Class B1 or A), that would fall under the private route, which means you'd be paying private rates. A friend of mine who delivered at KKH mentioned her C-section in a private room came up to around $9,000 or so, just to give you a rough ballpark. The good news is that even the B2 ward is said to be reasonably cool, so it may not be as uncomfortable as it sounds, though I know that's very personal preference especially post-surgery. My suggestion would be to call KKH's patient services directly to ask about upgrading options, as sometimes there is flexibility depending on bed availability, take care of yourself, and wishing you a smooth delivery!