Your current stone mantel is built into the stone. Are you planning to change all the stone? If not leave it be. If you feel you must change it get a piece of wood the same thickness and use matching corbels. I would not touch it as the hearth is the same material. None of what you have posted will look right in my opinion. The time to address changing this was before the conversion to gas.

I need to see your room how would we have any clue as to what to do there with no context I like the simplicity of the boat but I need to see the sapce . Post the pics here in a comment .

I really like the simplicity of your mantle - what about it is not working for you?

I added a photo of the room.

" I added a photo of the room. "

Even more reason to leave it as is. Anything you do to change it will make it look like a hodgepodge miss.

Am assuming the last photo is your room and fireplace. Is the stone just applied to the wall? The fireplace itself just looks disconnected from the shelving. If the stone can be removed would suggest you do that and then make the entire wall into a cohesive composition of cabinetry and fireplace.

^ agree but I would remove the cabinetry or if there is no flooring beneath it, I would cut them down and create closed storage

fireplace is nice, shelving is way too high, out of proportion