Hi mama, I can really understand your worry given what you've been through, that's a lot to carry into another pregnancy. From what I hear, KKH's subsidised route actually has really strong support for high-risk cases like yours, and they do assign you to a dedicated team for pregnancies with complications. The cerclage procedure itself is fairly routine at KKH, so your doctors should be able to plan around that timeline quite carefully.
As for hospitalisation leave, it's definitely worth asking your doctor directly, some mums with similar histories have managed to get extended medical leave leading up to procedures, but it really depends on your specialist's assessment and what your employer's policies allow. Someone in my mum group mentioned that being a subsidised patient at KKH works really smoothly for high-risk monitoring because you get consistent care without the gaps, which honestly sounds like a plus for your situation.
I'd say have a frank chat with your KKH gynae about your concerns, they'll know exactly what's reasonable to request and what the evidence shows for your particular history. Wishing you all the best with this pregnancy.