Disclaimer: I'm sure everyone has somewhat unique physiology and other circumstances when dealing with fissures. What worked for me, may not work for others. However, I believe things that ultimately worked for me were simple enough that I can see them work for at least some other people or they can provide them with at least more sample points to consider their options.
What worked for me consistently:
1) Using enema bulb every evening with regular clean water and lubrication
What I used:
Enema Bulb: https://www.amazon.com/dp/B078S3C5S2
Lube Shooter: https://www.amazon.com/dp/B008ASBIU0
Water based lube w/o additives: https://www.amazon.com/dp/B0161J28AI
I noticed that using a Enema Bulb with regular tap water EVERY day before sleep WITH lubrication (using lube shooter) to avoid any insertion injury or pain makes the next morning stool very consistently soft for me regardless of my diet (even if I drank alcohol and ate chips). It was by far the most effective method for me in controlling softness. I've tried vs Colace, Miralax etc.
My theory is that if you do not empty bowel before you sleep no matter how little there is, the matter that is already down there dries up while you sleep forming into a denser dryer mass. I never noticed any habit forming and always had normal stool in the morning afterwards. I tried to find information about using bulb enema's with regular water to just quickly clean out the bottom of the colon, and didn't see much concern unless you use actual laxative formulas (i.e. fleets).
Process: Load lube shooter with lube. Carefully inject its contents into rectum subject to tolerance. Ideally inserting it a little bit to make the lube goes in. Fill the bulb enema with comfortable temperature clean water and slide it in carefully. Squeeze it gradually to empty it in. Wait about 30 seconds at minimum and go and let it go. Water and lube should in theory help reduce any irritation you may have there. (This gets much better over time as things continue to heal)
The method above really worked well for me, but it did require a loyal daily application. At one point I slipped and skipped one evening and immediately got a bloody re-tear the next morning. This taught me two things - the method really works for me, and that I want to see what else I can do to remove this daily dependence. This inspired me to focus on another thing that worked wonders early on but what I did not do consistently. The dilation I describe below allowed me to stop doing the water bulb enemas daily and I only now do them after days when I eat and drink a lot and suspect problem may come.
2) Manual dilation to decrease the tension and increase the "throughput"
What I used:
Vibrating dilator set: https://www.amazon.com/dp/B074BCFB8J
Silicone based lube: https://www.amazon.com/dp/B003CP153Q
Cheap non-lubricated condoms: https://www.amazon.com/dp/B0078OZBKA/
I've read on this very forum first time about benefits of dilation and it made theoretical sense. The key problem here is the "cold start" that is to start with it when you are already very tight and in pain. I first tried this method after I struggled with combined thrombosed hemorrhoid AND chronic fissure for about 6 months and almost gave up on non-surgical options (tried nifedipine, diets, creams etc).
At first I also used same water based lube as mentioned above. It was not messy since it was water based but I also found it didn't work quite as well as silicon based one.
I found that vibration was helping with insertion better than those that don't. I also found the sizing to be pretty good. I felt that the smallest size was not much larger than a finger, so a good strategy for me was to start with my own finger (covered in latex and with lube ofcourse). I bought super cheap non-lubricated condoms to put on the dilators to ensure both cleanliness and eliminate any scratching from surface imperfections on the dilator.
For me personally the path was: Start with your own finger and just gradually work your way up. After a week of doing this every day I worked up to the largest size of the dilator set. It looked crazy large when I first bought the set, but body can do magic sometimes. Key is to take it slow and try to do it when you are least irritated down there. For example, if you just had a re-tear, try to first manage it with diet and let it calm down. Some mild discomfort is OK, but everyone's physiology is different. I read somewhat that some people use lidocaine - I did not. I felt it was better to feel what you are doing down there to avoid making more damage.
To maintain the tension I now use the dilator every 3 days before sleep and don't pay much attention to my diet anymore with regards to the fissure. I always start with small and work up to large for about 20-30 minutes, then wash it all out with a soapy enema bulb due to usage of the silicone based lube. I still do use the regular water bulb enema on days I can tell things can get too dry.
My general finding is that chronic fissure underlying issue may never quite go away without at least some maintenance. I can feel that the surface/tissue is forever different down there. I do think that having a process that keeps things in check helps not only to keep the fissures at bay but also mitigates other potential things that can always otherwise flare up down there.
Hope this helps at least some folks. Keep fighting!