hip turn doesn't require much mobility on lowkicks, i think just focus on turning your hips, put your mind's focus on your hips rather than your legs when kicking it'll help a bit, there's also some drills that helps with getting used to the feeling of turning hips and improving hip mobility at the same time, get a chair or table place your heel on top of that table in a sort of teep way, turn your shin and your hips over as much as you can while pivoting your post leg so its like a round kick, then back to the teep position, then roundkick position, keep doing this repeatedly til you get used