BA flex tickets

[Phil001]

Hi
I’m new to the forum so please forgive me if it seems like a dumb question.
I’m looking at booking some flights to Orlando next easter (2026) for a trip following a serious illness in the family.
This may need to be cancelled and I see that BA offer 3 Premium Economy flexible options – semi-flex, flex and fully flexible.
The flex seems like good value and says it is refundable but it doesn’t say what the terms are (fees, time before flight etc.) and despite a lot of searching online I can’t find an answer that I’m confident in. The fully flexible option is about twice as much as the flex.
Does anyone know what the difference is or is it best to ring BA?
I’m currently a Silver member and am also thinking about using Avios for some of the seats. Am I likely to find any seats on such a popular route next Easter?
Thanks