Health Insurance / E-CARD in Austria for Retired?

Hi,

My wife has just registered in Austria for residency and has received the "Anmeldebescheinigung" (confirmation of registration). I will be moving there later in the year and we are planning to live there permanently. As part of the registration process, she needed to provide proof of ability to support herself (we are not planning to work there) and also get an E-CARD for health insurance. As we had not sorted out health insurance yet, the registration was accepted on the grounds that an E-CARD would be submitted later as proof of health insurance.

My question: is it possible to buy private health insurance and somehow link that to an E-CARD, or do we need to buy health insurance from the local district / authority. I understand that there are different types of schemes / funds in Austria but they tend to be for employed sectors. What are our options as people who are supporting themselves?

I have seen one article on wien.gv.at that says:
Self-insurance
Persons not covered by compulsory insurance may take out voluntary (self) insurance. Contributions for voluntary insurance are EUR 397.35 per month. If the E-CARD is mandatory, then self insurance does not seem to be voluntary?

Is there any way that a UK EHIC card can be substituted for an E-CARD?

I know there are UK companies that sell health insurance for Austria but they don't seem to know what an E-CARD is.

Thanks
Nick