Purchasing the insurance now... Be careful. You might be able to purchase it, but the "pre-existing" condition might be problematic. As a frequent purchaser of trip insurance on my "bigger" trips (European cruises, week in London at a rental house, etc) I have utilized it a couple of times. Most recently almost had to because of PE (blood clots in lungs) in Dec 2017, with the London trip planned in July 2018. Hope it works out for you. Good luck.