I've never heard of an IWB holster with a retention strap, and I think that's because there's almost zero market for them. The reason for a retention holster is primarily to prevent someone from taking your gun, but if you're carrying concealed that shouldn't be an issue because nobody knows it's there in the first place. As far as keeping the gun from falling out on its own, a good concealment holster has adjustable passive retention at the trigger guard that will keep the gun in the holster even if you trip and fall down the stairs (don't ask me how I know this). Drawing from concealment is more difficult and time-consuming than drawing from open carry, and adding an unnecessary strap to the draw process is a bad idea in my opinion.
As for the night sights, I see them as pretty useless in most situations, which is why I buy sights that have a good daylight sight picture and I figure the tritium vials are just a bonus. There's a very short period of the day where night sights are useful, and that's during the short period where it's dark enough that it can be harder to see your sights but still bright enough to identify your target. If it's too dark to see your target, then you should use a flashlight or some other source of light, and at that point the tritium usually isn't visible and isn't needed anyway. For me, the primary advantage of night sights is that it makes it easier to see exactly where your gun is on the nightstand even if the room is pitch-black.
My favorite type of defensive sights are Trijicon HDs. They have a big florescent dot in the front and a large black U-notch in the rear. I like them because the rear is just black so your eye is drawn to the front sight only, and the rear U-notch is wide enough that the front sight is very quick to pick up. Also, many sights don't give you enough daylight on both sides of the front sight when the gun is farther away from your eyes (like in an iscosoles stance), but the U-notch is plenty wide on the HD sights so that's not an issue. Oh, and the HDs have one tritium vial in the front sight and two in the rear, which is a bonus.
