Here is a second vote for the Wilson grip safety. Though keep in mind that even though the part is labeld as "Drop in" it may not. I recently installed one of these and I needed to some adjustments to the safety to make it fit properly.
I suggest that you call Wilson Combat to order the safety and discuss with them the pistol you have to ensure getting the correct part. Plus, depending on how familiar you are with doing a complete disassembly and reassembly, you should also get the book and video on 1911 maintenance. These contain clear instructions and good photos to show you what to do.
Finally, I suggest that you become familiar with the disassembly process before trying to change any parts. So wait to do the replacement until you can disassemble and reassemble the pistol without using the book or videos.
Rest assured, there will be some fitting involved, not to install the BT safety, but to get it to properly function. However, if you can use a file, you should be able to handle this job. Use your factory beavertail as a template and go slowly. Most of these parts are made slightly over-sized so that they can be properly fit.
The Wilson Combat drop-in is, as already suggest, a great choice. I've included a couple pics of the Wilson BT which I installed on my Commander.