Someone at the bank told me to buy
trip insurance just before I go and then cancel it when I get back, if I didn't need it, but that doesn't sound right.
I assume she means a multi-trip type policy (similar to annual medical)? She is making a couple of unlikely assumptions, but you might find a policy that would allow that.
First, you would have to watch carefully for the meaning of "just before". Almost all trip insurance has a long elimination period to prevent people from buying it once they discover that they can't go. I would expect at least 90 days maybe more on any policy. Many I have seen are tied to the date of the first payment for the trip (i.e. within two weeks of your first payment, or that particular trip is not covered).
Second, you would need to find a policy that refunds some of your premiums if you cancel part way through the term. I would think that would be almost impossible to find for the first year, perhaps in subsequent years if it is an auto-renewing type policy.
I can't think of any way that this would work on a single trip policy, which is what I would recommend.
Again, read the terms of the various policies available before buying so you know what is covered/allowed by the policy. Insurance companies are generally very rigorous about applying their rules. Remember their primary objective is "return on investment for shareholders", not helping people.
Finally consider if you can cover the risk yourself. This is an expensive trip for you, so probably not. Personally, if I were to cancel a trip (to an Orlando timeshare) I would be OOP at most about $1000. But I will probably pay more than that for insurance over say 5 years (@ $200/yr). So what is the probability that I will cancel more than once in a 5 year period? Pretty slim. I generally just take measures to limit my exposure where I can (refundable tickets, cancellable reservations) and take my chances.