Displaying features by multi-attributes using proportional symbols

I want to display my features by using multi-attributes. I dont want to use catogories for the symbol size, I would prefer proportional symbols. I know it works pretty well for classifying the symbol size, but I want my second value to be displayed by proportional symbols. Is this even possible or do I just have to be content with categories?
I am using ArcGIS Desktop 10.5.1.

Thanks for the help!