Agree with Cornish Frog Boy, we book in a very similar style.
A condo Or apartment rather than a villa is probably easier to find with more hotel style flexibility with changes/cancellation . Floridays springs to mind But there are plenty of others.
Americans tend to book far later than us so booking a villa far later is certainly an option (if we do this I tend to have a cancellable condo or hotel fallback booked). Does depend how flexible you can be with area though.
Our current flight bookings have been rebooked several times .
They started as been booked for September this year as a cheap hand baggage only fare for around £340 pp , I then moved them to next May as a main cabin fare with bags included , this was a free change and moved to the slightly more expensive £480 ish fare because that fare offered free change of dates and route for far longer than hand baggage fares did, Ive just moved them again to the end of August next year , the fare was a bit cheaper so I could have had a small credit but as it was only £60 more out in economy and back in premium economy I’ve booked that for more comfort and two bags back instead of one so a bit more shopping is on the cards
(I will pack a big nylon hold-all so the dirty washing will be packed in that leaving space in the cases for the new purchases).
These are all direct flights with BA but booked with American Airlines as their change conditions are more generous than BA’s own.