Insurance with cancer

In the middle of buying our house in France I was diagnosed with cancer. I’m still the middle of treatment in the UK but I would like to do at least part of my recuperation in France and then start using our property as we intended. I’m UK resident so I have no access to a French resident’s healthcare entitlement but I’ve got EHIC so for now the basics are covered.

I would be interested in what additional insurance others in the same position feel it wise to take and which companies are the best to approach? This may become even more important following Brexit as proof of health insurance cover is a condition for the granting of a long-stay visas for non-EU residents. Thanks