Another option I think worth looking at is increasing the thickness of the glass without going to the double glazing - is that what "hush glass" is?
I think it would make a big difference we did this in our bedroom windows and it made a big difference. Double glazed with one pane of the glass being “hush” glass we never called it that, but basically it was safety glass, my understanding is one of the panes it was glass then some resin to dampen the noise then a second pane of glass all Moulded together. Then a second pane of ordinary glass
This is one version of Hush glass, called vlam hush, andibasically has a laminated interlayer . I was going to use something like this on a project some time ago, but wasn't needed in the end http://www.viridianglass.co.nz/products/noise/vlam-hush