I am the same size as you are, but about 10 pounds heavier. I make do with my shower/toilet. My son has an older 5th wheels with a bubble skylight over the bathroom that gives about 10 to 12 inches of additional head room in the bathroom. It has a milky finish so people can't see in. It would be much easier to install that the bathroom mods you are presently considering. I think any of the box store skylights would work, pretty easy to caulk.
As for the inside walls of the TC being load bearing, I do not see them load bearing like in a stick house. They do offer roof support simply because they go from the floor to the roof, so by default the help support the roof. When I walk on my roof, I try to keep my weight over the walls and floor to ceiling cabinets. Definitely less movement there. I have seen older TCs roofs sag in the center span, but not where the inside walls are. It sure does not mean the roof will fall in by removing the bathroom wall, but the roof will not be as strong.
As I previously said, I would look carefully at the skylight. I think that would be a better choice. If you wanted to do so, you could use one skylight to do part of the bathroom and go over to another part of the TC. Many shapes of skylights are available.
Wayne