Get customer info on sale of different products

I sell three products. The basic product is the same but I need to collect different customer information depending on which product they buy. If I set up custom order fields all the fields appear on all the customer orders. If I set up custom item fields all the fields appear on all the products. I only want some on each of the different order or products. Can you help me?

Hello,

If I set up custom item fields all the fields appear on all the products

The solution will just be to :
- Create a un-published category
- Add the product which should display the custom item field on that category
- Add that category on the "Categories" option of your custom item field's configuration page.