Business sellers do not use Simple Delivery and choose their own postage.
For private sellers the only opt-outs allowed by ebay are for some letter or large letter items under £20/100g (excluding the buyer protection fee), for items of £750 or more, and items bigger than 120cm x 80cm x 80cm or heavier than 70kg.
Simple Delivery covers sellers for loss and damage in transit for up to £750, regardless of type of postage used. So no need for Special Delivery.