If you go with one of the usual suspects such as a Surefire X300
XYZ, Streamlight TLR1 or an Inforce, they should all work in a Safariland 6 series that is light compatible. You will then just need to decide your attachment method and level of retention. The Safariland model number scheme can be over whelming but all the attachment methods are interchangeable. The 6 series is also lined with safarisuede which will help protect the finish on your 1911. I have the 6 and 7 series for MANY of my pistols and I can interchange lights with no fitment issues. The 7 series are great, although I have not seen on for the 1911 with light. I do how ever prefer the 6 series. They are a little more refined and the suede lining is a nice touch. As for retention, there a several options and the holster you choose will likely come with one of three options.
1. ALS only, this is a tab that you activate with your thumb and locks on to the ejection port of your pistol. It automatically locks when you holster your pistol.
2. SLS, this is a hood that covers the back of the slide and is rotated out of the way manually to draw. It must be manually reengaged when holstering.
3. ALS and SLS, this is most common in duty holster used by LE. It is a combination of both.
Here is a video that demonstrates the ALS and SLS systems.
Here is a video the describes the different belt mount options.