I had exactly the same issues when I installled the KW Comfort kit last year. Turns out the front springs were too soft. With the stiffer springs (#2041 instead of #2039), it was a night and day difference, I have not bottomed out at all. See details in this thread, my posts are from #18 onwards:
https://f30.bimmerpost.com/forums/sh....php?t=1799518
Another factor may be that you have the spring perch too high. The specified range by KW is quite narrow, 7.3" to 8.5" from the centre of the knuckle bolt. Paradoxically, the car rides better if you are lower, as the spring is in a better working range.
You might also be interested in this clip by
FaRKle! about using different springs, in his case #2025 from the M4 convertible
Swift springs seems to be a common upgrade that I have seen on various forums. Here's one on e90post:
https://www.e90post.com/forums/showthread.php?t=487445
Keep in mind if you change the fronts with a drastically different setup, the rears will need to be swapped as well.