I think you're overthinking how to wrap/send the Magic Mum swaps.
I've received in the past swaps that were wrapped in a deconstructed Dunnes Stores paper shopping bag, in wrapping paper (though how that managed to stay in one piece through the entire postal service I'll never know), in brown paper, in padded envelopes, in Jiffy bags, in mail bags and so on.
So long as what you're sending is protected (I'd suggest getting some bubble wrap if you don't already have it) then just putting it into an envelope of the relevant size should be fine.
These might be useful:http://www.envelopes.ie/section/863/1/c ... b42098e6e5
or maybe these:http://www.envelopes.ie/section/496/1/w ... -envelopes
Don't worry about the finish on the shoe box, if that is how you're planning on sending it. Just make sure that it's well protected would be my advice.