Hi Beth! I'm sorry to hear about your problem. I've had a permanent ileostomy for a little over 21 years now. I remember having a similar problem after my surgery. I have a flush stoma too. My skin was very sensitive, and I developed rashes. I also only use Coloplast products. Fortunately, I had an excellent wound care nurse who helped me figure out things along the way. These are some of the things I do, and while I understand that everyone is different, and some things may not work for you, I'm hoping that maybe something will be helpful.
1) Stomahesive powder really helped me with the rash and the red ring. It can still sting when applying the appliance with the paste, but it heals quickly, and by the time I had to do another application, it wasn't a problem.
2) Because you want to make sure that you're catching the leakage as soon as it occurs, a two-piece appliance makes it easier to see what is going on, than a one piece. I use the Coloplast 2 piece Assura cut-to-fit convex Extra Extended Care. It gives me more control of the shape of the hole, as my stoma can be somewhat oblong when it is at flesh level or beneath. Sometimes my stoma doesn't want to come up, even with a convex wafer, but it still helps to prevent leakage.
3) Some pastes melt too fast or are too loose? I've tried multiple pastes, and the only one that I can use is the Coloplast Stomahesive paste. I've tried the Coloplast Brava, and it has a different stiffness(?) to it. You don't need a lot of paste. Apply the paste slightly further back from the hole in the wafer because if you don't, as the paste sets on your body, it will slide through the hole and cover the stoma because the stoma is flush with the skin. I also learned to prep the wafer and let it sit for 30 minutes to an hour before applying. It helps to make sure that everything is dry, but not too dry, so that it holds it's shape and won't seep beneath the hole in the wafer. It's also helpful because of #4.
4) You really don't want that wafer to be able to move or slide so that the stool can get beneath the paste. I faithfully use Adapt Hollister Medical Adhesive Spray! It was the game changer for me, when the nurse suggested it. I know you say you are allergic to most products, but maybe you can look to see if there are ingredients within this product that you are not allergic to, because that was the main thing the nurse suggested that helped. It is not the same thing as a skin prep spray. It is very sticky and moisture resistant. I've tried to see if I can find another product that is comparable, but I haven't found anyone who makes it but Hollister. Unfortunately, I did learn that Hollister discontinued the spray, but you can still find it online in multiple places such as Amazon, Ebay, and some online medical stores. I am very upset about this, but I plan on stocking up on it until I can find something comparable. One can will last you quite a while. I spray it all over the wafer after applying the paste, and let it dry.
5) I also use a skin prep, but if I'm dealing with a rash or broken skin, I use a non-sting wipe. Make sure it dries out completely before applying the appliance. Apply it right over the stomahesive powder. When my skin is healthy, I use Skin Tac Liquid Adhesive. It helps to maintain a strong bond with the medical adhesive spray. I can get a wear time of at least two weeks, but I have worn an application for as long as 6 weeks. Because I'm using a two-piece system, I only have to change the bag out once a week to every two weeks.
6) The placement of your stoma can make things complicated. Mine is right under my waistline, so the wafer is right where my skin folds are when I bend. After I place my ostomy on, I wear an ostomy belt to hold it in place until it sets completely. It helps for when the skin seeping causes the wafer to not adhere all the way. Usually I wear it just for a day, if I change it in the morning. I'll wear it over night, while I'm sleeping, if I change it in the evening. I've gained pandemic weight, so I do have to wear it more, just because of my fat folds. :( It might be helpful for you to wear one all day, and all night for extra security until your skin heals.
7) When I change my ostomy, I wear loose clothing and underwear. I used to wear tummy control underwear, or tight pants to hold it in place, but that will cause stool to accumulate right at the wafer and seep out beneath the paste. I can still wear these things, but I make sure that the the appliance is set for at least 24 hours before doing so.
8) When I did have leakage, it tended to happen more at night, while I was asleep. I really had to pay attention to my bowel habits because I don't want to have too much output while I'm sleeping. Ballooning from gas made it come loose real fast. Also, while lying down, heavy stool output can accumulate right around the top of the wafer, which will break down the paste more and cause stool to sit right on the skin.
I hope something in that was helpful to you! Good luck!