Hello Marie,
Because I also fly across the pond to Walt Disney World Resort from the United Kingdom and can shop for England - I totally understand your very important question!
It certainly is tricky to make sure all your beautiful Disney purchases are not only packed securely, but also won't take your luggage over the airlines baggage weight allowance.
My top tip is to always
pack-light by packing only a few outfits and not an entire wardrobe of clothes as this will ensure you've plenty of space for all those lovely new purchases; plus, don't forget to include a set of luggage scales!
In addition you might not realise that Disney Resorts do have Guest
Laundry Services so there's absolutely no concerns of running out of clean clothes whilst on holiday.
For up to date information on shipping items back home to the UK from Walt Disney World Resort I suggest contacting
Disney Merchandise Guest Services directly via this email address - Merchandise.Guest.Services@DisneyParks.com
I also thought you may find this
Disney Parks Blog ~ Answers to popular questions about shopping at Disney Parks to be an extra useful resource.
Have a great Disney day.
~ Jane