We have just completed the 7 night (8 days) Nth Qld cruise from Brisbane. This was a short cruise for us, less expensive and with the ship providing Covid coverage and both of us being covered on land by Medicare, we decided that this time we would take a risk and only take out the Bare Essentials Cruise policy offered by Insure & Go, which really only covers for evacuation and shipboard medical expenses (other than Covid).
Our medical details are almost identical to yours. One of us aged 75+ and the other younger with the above diagnosis and treatment within the last 2 years as well as coronary artery disease. The premium was $251.29 of which $197.09 was for Travel plus $54.20 for the additonal special medical coverage.
Covermore cover for lots of things including cancellation costs but we thought that if we had to cancel because of Covid, we would at least get a Future Cruise Credit from the Cruiseline.
Luckily, we didn't have to claim this time, but Insure and Go have previously reimbursed us for shipboard medical expenses and missed ports on overseas cruises.
Sometimes you get a discount online by using a promotional code.