TILE
In your master bath you have a chocolate travertine which comes in all kinds of options. Tammy, Jen or Debbie at Baptista tile can help you find a good color match for the existing stone you have in your house. After contemplation of the challenges in your bathroom composition the most cost effective solution I could come up with is this: Using a chocolate travertine chair rail and completing chocolate travertine 12x12 to frame out your tub windows where there is now wood. Use the same 12x12 travertine to refinish the floors. Also, for fun you could make open frames to hang over your mirror out of the same chair rail to visually define the sink space a little. I can help you determine the shape and size that could work best for this if you like the frame idea.
MASTER FIREPLACE
In the tight corner a fireplace like this might layout better than your existing unit. I have a link to a supplier and the owners manual in the lower corner of that link has the dimensions and installation information for review. I didn't take dimensions on my visit but by best guess says this could be a good solve. We also talked about a cement fireplace surround and the link to Cement Elegance is below. They have directions to their showroom on their website.