How long should I bake my oatmeal cookies?

I’m trying to make oatmeal cookies for my children, but I always end up with not-hot enough cookies or burnt ones. I bake them for 20 minutes usually, but my friends tell me to do 15 minutes. I do that, but doing that makes the cookies not hot enough. What do I do?

Also-- I use a Black & Decker toaster oven. The cookies are about the size of a poker card. But seriously, I don’t know where to buy oven thermometers. I don’t think they sell any here in Texas.

They even sell them here in Thailand; I am sure they sell them in Texas. Try a cookware store of True Vale or Ace Hardware.