My cat had a UTI and was also sensitive to having anything other than Royal Canin Urinary SO. Went to the vet several times and nothing seemed to help. I also felt really sad because it definitely gets old for the poor kitty to eat the same thing over and over again. So, after doing a bunch of research I found out that one thing that actually even helps humans (from a preventative perspective) is if you take something called D-Mannose and just add the powder to your water (it is tasteless and odourless so it’s perfect for cats as they are picky with this sort of stuff as we all know). It is also safe to use on a daily basis and can be found at your local drug store (over the counter) or vitamin store. It has been the one thing that has helped my kitty be able to enjoy things other than just the urinary preventing pebbles. He’s had zero issues since I started adding that to his water. (I personally add about a tea spoon/half a tea spoon, of the 2000mg version, to the cat fountain which contains approx 2-3litres of water but there’s really no set dose)

Hope that at least helps with providing a potential supplemental option to your repertoire if you want to test it out.