I work on something similar and wondered about that as well. I wanted giant stars and supermassive black holes to be perceived as incredibly huge (which they are). My thought was that any star would "look" and behave the same if you simply stood further away.
Meaning: A star with the diameter of 10 at a distance of 50 will look the same as a star with a diameter of 1000 at a distance of 5000. But there are two things to consider:
- Giant stars have a very low relative mass! Meaning while their radius is thousands of times larger than that of "normal" stars, their mass is merely a multitude of several hundreds as large. Meaning their gravitational effect is much lower, probably causing planets to revolve around them much closer - relatively. Their lifespan is therefore also much lower, because they effectively burn their mass much quicker than other stars.
- The speed at which stars pass by as you move in space is essential (especially FTL). If you see that normal stars pass by as visibly small objects around you, but some stars just appear to be almost static even though they are of similar size on the screen - their size is perceived as much higher.
- Seeing large objects already at a large distance moving much quicker than even larger objects behind them also contributes to the sense of scale. Meaning: Flying past a star and seeing a giant star behind it will cause the star in front to move relatively quickly. This clearly indicates that the giant star is indeed gigantic. This plays together with number 2.
So movement is probably the best way, and the setup of the solar system the other. One scenario I can imagine is that giant stars have plenty of planets revolving around them (their mass is still high) at much closer range. It's possible that this is not scientifically accurate, but from a visual and worldbuilding perspective, it might be feasible solution.
