Track referers / leads

Hi, I’m hoping to find some help here. I have a form selling one product and I’d like to award partner websites that send customers to my site.
Sounds like an affiliate system, doesn’t it? But that’s way too much. I don’t really need all the features of an affiliate system. I just want to know when website abc.com has send me a user who submitted this one form.

Any ideas what I can do?