I've done a few kettle sours and it works well if you can maintain the temp and then boil it when you are happy with the pH.
I did read about a Berliner Weisse where you splint the wort into 2 fermenters - K97 in one at 20 degrees and Lactobacillus into the other at 35 degrees. You then combine them once fermentation is complete and condition them together.
Never tried this but they say it makes for more predictable results.
I didn't have any problems with kettle souring.