You definitely need ambulance cover, but that can be provided by the service provider, you don't have to join a fund. We have complete cover for all calls with SA Ambulance; some health cover provides cover for only emergency calls. The fee is generally around that quoted to you.
My husband was referred for a cataract operation within the public system in Jan last year and it was done in March. I have several friends who have had similar wait times, through the Repat Hospital in SA. Perhaps you could ask for a referral to a public hospital with lesser wait times. Cataract surgery here is day surgery and often not rebateable.
You can get insurance through not for profit funds, like HCF, which cover you for certain chosen services, and you can elect not to be covered for some, like obstetrics, that you will not need.