Fireplace Damper Advice

I've removed a very dated looking fireplace insert from my masonary wood burning fireplace and I've discovered that there's no damper. I'm looking into how to replace it. I've been looking at the types that fit over the top of the chimney but I'm thinking it'd be cheaper to just install a standard steel damper above the fire box. There's a ledge where the original damper would have sat. I'm wondering if anyone on this board has any experience replacing a damper? I'm likely going to call in a chimney sweep/contractor but I'd like to be armed with some knowledge before I commit to anything.

Thanks in advance.

There should actually be two ledges - one where the damper was/shouldabeen installed, and one above that called the smoke shelf. The smoke shelf serves to stop cooling smoke from falling back all the way into the fireplace. It hits the shelf and gets deflected back into the rising hot exhaust stream.

I would look for the oldest mason you can find and have him look at it. New, actual all-masonry fireplaces are somewhat of a rarity these days and the younger guys may not have the black art / skill of building them properly.