If you really want two optics, I would definitely go 45° rather than on top of another optic.
There are many options, smaller is better (and lighter). Look at the already mentioned Trijicon RMR, Docter, J Point and Vortex Razor Red Dot.
Once again, try a variable power scope, it will do everything that you want it to.
If you are dead set on a red dot, look at a primary optic with increased magnification. 2.5-10x32 for example.
Bookmarks