So I made a compromise between making the Luma bigger and more pixeled. He is bigger but not twice as big, resulting in a more bulky shape.
Edit: For this test I only modified the right moving graphics. The lower part of Lumas eye is not completely black to make it look less big. When it was all black it looked worse. What I did is also used for the SMB2 Peach in some graphics.
Personally I don't really like it. I also tested a little more playing with my original version, and usually there is not really a problem with that. Especially not with the force field effect. Actually for the force field this effect actually makes it smoother.
The only small problem is the eyes of the Luma. In normal horizontally scrolling levels it is not a problem, since the player moves with the screen. Only when you are at one end of the level or in a level that does not scroll horizontally at all. Since I replace Link, she will also naturally bounce, changing height all the time, I think this effect slightly distracts from the negative effectl, so when you are running you won't notice it (at least on my screen, maybe it is different if you have a much bigger screen).
Only when you stop completely at the wrong moment or make one baby step after another and focus on the Luma just to see it, you will... One eye will be a little thinner, that's the only thing you will notice. Something you can actually notice with 2x2 pixels, too. It is just more noticable with a 1x1 pixel.
Overall that is just a minor flaw to me, that as I said won't be noticed most of the time, as long as you don't try to find it on purpose. You focus is more on Rosalina herself and what is infront of her, rather than the Luma.
For me it is about on the same level as problems like the hitboxes of some (if not all) default characters being two pixels off in one direction. (When I touch a wall on the left side, the graphic goes further inside the wall than it would on the right side)
If I am finished I will post it and hopefully will get feedback from more people.