I posted something similar a few years back, when I got the newly released HK45. For what the gun costs, you'd think they could put something on that didn't need a flashlight charge before it was usable in low light.
My HKs run Heinie straight 8s, yellow back, green front, and I am a fan.
For bad eyes and less precise placement (though still on the mark inside 25 yards or so) look at the XS big dot sights. I have them on other guns and they are quick on target, but less precise on round placement than a smaller aiming point up front.
Another option is a laser; however, if you go to laser, train, train, train. Once sight alignment and sight picture are truly ingrained, laser is a whole other game. But, rapid on target and easier on the eyes. And not entirely comforting for the target-ee.