We have used GoodToGo this time as they didn't seem to expensive and cover all our pre existing conditions. There are also companies like Staysure and Allclear.
It's 4 years since I last took out any holiday insurance. At that time, just before my 65th birthday, I paid about £16 for European cover for a full year. Their prices have gone up somewhat to take Covid into account but they might still be worth a look:
https://www.holidaysafe.co.uk/