I was wondering if something like weight would work, I'll just have to find a way to hold them while I do it as I usually put my hands behind my head, so an adjustment will probably need to be done.
I'm not a trainer by any means, but I would see how it works to not use your hands like that. Many times it forces you to pull up on the head, which can hurt your neck. Your neck and head should be in a straight line with your upper chest. When doing regular crunches, I usually have my hands or fists next to my ears with elbows pointing towards knees.
Holding a weight can be awkward and painful at first, but once you get used to it, it should be no issue. Make sure you are keeping nice form when you do them with the weight.

