new with a question

As far as I'm aware, curl defining products aren't going to give you curly hair if your hair is straight.  They may just have some benefit for already curly hair (if I'm wrong, somebody tell me, but I think they are mainly anti frizz products that may lock some moisture in the hair shaft, which would make already curly hair tighten up a bit).

I don't think there's a way to curl it without at least doing something.  If you don't want to use heat, or buy curlers, you can braid it, or use stuff around the house.  One way I do my ends is to wear it in a bun, especially if I put some gel in it first and bun it damp, it will stay curly for a  little while after it dries and I let it out.  If your hair is shorter you can try wrapping the ends around something and pinning or tying it in place damp and sleeping on it until its dry.  You could use bobby pins or strips of cloth to shape it into curls for that.