I had difficulty finding holsters that will accomodate the 1911 with ambi safety. If the holster has a retnetion strap, the strap would be a little short in snapping due to the extended widthof the gun. Not one I tried worked well with ambi safeties.
Finally I ordered one from a man in Magnolia, AR. He built a holster at a very decent price with a strap, full tooling and it worked well.
However, I use many different holsters with time. What I need one day may not be what I need the next. Therefore I found a solution that works with every holster and does not interfere with retention.
Take an exacto knife and make a cutout for the right side safety. A photo is shown. Just cut exactly what is needed. The holster will retain it's shape, the retention strap will work and the gun will hold secure in the holster.