I got the jumper in a size 20 and it fits me but there isn't much extra room so I'm not sure it would work on much larger bodies but its always worth a try if you spot one in your local Primark.
The jumper is quite thin so it will work for the spring too and for only £10 you can't go wrong. I have lots of MLP brooches so I'm thinking of adding one of those the next time i wear it.
I have seen online that there are lots of different MLP pieces in Primark but this was the only one i could find in my local one. Have you got any of the pieces?