Your mom is exactly right. Props to her for not simply freaking out about getting stuff online. She HAS a valid point.
Just go get your eyes checked out by a doctor. Telling you right now.
Your eye is a sensitive and unique thing. You need to know what you can and can't stick in it. You need to know at least your base curve and diameter, and that's if your vision is already perfect with no astigmatism. Your doctor will also show you and make sure you can put them in AND take them out.
Then you can take that prescription and order contacts online.
After that, there are places like PinkyParadise and HoneyColor. Most of their contacts are from 20 to 30 dollars for a pair and they last a year.