16 cat with chronic recurring cystitis

My 16 year female cat suddenly out of the blue developed cysitis about a month ago. This started one evening with frequent trips to the litter tray with nothing produced and then small amounts of bloody urine being passed, when she was just lying down and lifting her tail to pass, in obvious discomfort. After a trip to the vet they decided it was cystitis or a UTI. She had a steroid injection and antibiotics. This then recurred 2 weeks later exactly the same symptoms, again trip to the vet and this time just a steroid and antibiotic injection. This recurred again a week later so another injection and this time 10 days of antibiotics. After this course of antibiotics I noticed that a couple of times she had blood in her urine so she is back on the antibiotics.

I've read that Cantharis is good for acute attacks of cystitis but is there anything else you can recommend. The vet each time has said the bladder is very small, they can't feel any lumps or bumps. She is eating well and her coat and eyes are good. Obviously she is an old cat the vet wants to do x-rays, I don't want to mess around too much with her at the moment as she is an old lady and it won't really be fair on her.

I'm desperate to try and stop these attacks recurring, especially as they are recurring so frequently. She is now on a urinary diet from the vet. Any homeopathic treatments you can recommend. I'd be so grateful.