Select a courier because this is a heavy item without changing all current listings to this courier

[sheberie]

I have a heavy item that I am unable to get to the post office. If I try and select the Royal Mail because they have the collection option, there is a message that ALL items listed now will  only have the Royal Mail. 

How can I select a courier for this ONE heavy item? 

[tommystrezures]

HOw heavy is the item? It would help if you told us so we can advise accordingly.