[Plugin Request] More image sizes

Hi all, I was wondering if there was someone out there that would make a plugin that would allow more image sizes to be specified in the admin control panel. I need more than thumbnail, medium and large. I see its been asked before:
https://www.ads-software.com/support/topic/235286
but I don’t feel comfortable editing my functions.php and I don’t know how to make my own wordpress plugin. Plus, I think from the read of it, you’d have to go in and change the code everytime you wanted to add/change an image size.

I didn’t see any existing plugins that could do this, please forgive me if I missed one that does.