Finder file size easy way
There's no perfect built-in macOS solution for what you want, and that's why macOS offers different view options. They each have advantages and disadvantages.

However, the closest option to what you want would be to enable the Show item info option. 

To do this:


Within Finder navigate to the folder you're wanting to view
Make sure it's in Icon view
Press commandJ (or just right lick on the window and select Show View Options)
Now you'll see the view options for icon view
Tick the Show item info checkbox





OPTIONAL: If you want this to apply to all windows with icon view, click on the Use as Defaults button at the bottom
Close the Show View Options window


Now you'll notice additional info is displayed below your icons

NOTES: 


The reason this is not a perfect solution in your case is that the info displayed below the icon is not necessarily the file size. That is, while for many files it does display the file size, for others it will display different info (e.g. if it's a folder it'll display the number of items inside the folder, if it's an image it'll display the image dimensions, etc). 
Not all file types will have additional info displayed.
I have found that sometimes you need to disable and then re-enable this option after copying items from another location across, otherwise the info isn't displayed immediately below the icon.


Despite the above limitations, enabling this will reduce the number of times you need to use Get Info to view the file size.