As advised, Simple Delivery covers the item for up to £750 for loss or damage in transit.
if you start your sale at more than £750, it won't be eligible for Simple Delivery anyway.
Personally, I would not sell those coins on Ebay.
You look like a fairly inexperienced seller and could be a target for fraudsters.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)