Do not be sorry for asking me questions that is what I am here for and I really want you to be able to help your son. If the wire is that stiff and doesn't fit in the vacuum hose it sounds like the wire isn't the right size. I just asumed that your are in the United States and #10 wire is a standard here.
You can email me at firstname.lastname@example.org and I can make sure that I get you the wire but I will be out of town until July 6 for the holidays so I would be able to mail it out until July 7th. Other than that the only suggestion I have is to take the vacuum hose to the hardware store and the size that fits perfectly in it would be the right size. I would say a #10 is just a little bit bigger than the size of spaghetti.
If you haven't read my previous message be sure and read it since it gives other options because you can use regular electrical wire. If you don't have the tools to cut the wire or strip the outer casing I'm sure the person at the hardware store would if you asked nicely.
Also the coil doesn't have to be worn tight around the waist. I wear mine loosly about my waist and it rest on my hips. I don't have any problem with it bothering me while I sleep but if it bothers your son make sure he wears it all the time during the day and remember it helps him sleep and he may just sleep and it won't bother him and once the pain is starting to go he will be able to wear it all the time.
If you can't get the wire please email me and I will make sure you get it.