Alternatively to using a potion, I would rather use some sort of NBT flag or temporary enchantment. However, I'm not really sure how feasible this is.

The alternative with using a potion is the ability to reduce the distance fallen every so often to compensate & to actually "slow fall" instead of feather fall. They might sound similar, but one of them actually makes you descend at a reduced rate (i.e., with an unimproved jetpack from various jetpack mods).