I think the key here would be to limit both – no buildings higher than ~6 stories (~30m) and a limit on urban boundaries, either enforced by land planning or economics.
Standard mansion blocks of six stories still have a much higher population density than suburban sprawling single-family homes while avoiding some/all of the issues with too high a population density – two-lane roads are usually quite sufficient and the sun does reach the ground from time to time.
See e.g. Berlin and Munich for (IMHO) decent examples of this.
I'm all for less sprawl but artificial limits like the ones you're describe would IMO only needlessly accelerate gentrification. For instance, it's very difficult to get a spot at a daycare in Munich, not because there isn't space in the system but because the city can't afford to hire staff that can afford to live in Munich.
Standard mansion blocks of six stories still have a much higher population density than suburban sprawling single-family homes while avoiding some/all of the issues with too high a population density – two-lane roads are usually quite sufficient and the sun does reach the ground from time to time.
See e.g. Berlin and Munich for (IMHO) decent examples of this.