I had a deeply inverted colostomy stoma, and the thing that worked best for me was this:
First, I applied a barrier wipe, then built up the surrounding area with stoma paste (which is like putty), and smoothed this out to a flat, slick surface by stroking it with a finger dipped in water. Then used half a barrier ring on top of the (puttied-over) divot in my belly skin where leaks happened most often. Then placed a flat wafer atop all that. Adding a snug wafer belt gave added security if I was going to be moving around a lot. I got to the point where I rarely had a leak and the seal was pretty durable. My stoma nurse was surprised I was able to get that thing to seal well at all.
Now I have an ileostomy with a normal, slightly small-ish stoma. I do a barrier wipe, then a full barrier ring, then a convex wafer with adhesive paste around the wafer opening; this gives me a great seal. But I don't think the convexity really helped with the inverted stoma - that shape is intended to cause a stoma to pooch out a little more above the surface of the wafer. There is no stoma to pooch with the inversion, and the convexity of the wafer irritated the skin around the stoma mouth, which always (in my experience) remained tender from output.
Sadly, I never found a good way to protect that area (the broken skin of the inversion around the stoma mouth). If you have damaged skin where you need to place the wafer, there is a helpful technique called encrustation (barrier wipe the area, sprinkle stoma powder over the damp skin, dab down the powder with another wipe and let a crust form. Repeat this again if the skin is very rough or sore. The best wipes for this IMX are Cavilon brand - they are sponge pads that hold a lot of barrier film liquid in them and make the dabbing/encrustation easy.
This protects excoriated skin and helps it to heal while wearing a pouching system. I tried this for a while also inside the mouth of the inversion, but it helped only briefly, until an hour or two of output washed it away, so that was a pointless exercise. I'm glad to have a normal ileostomy now; it is much easier to maintain and less painful than the inverted stoma was.
I wish you all the best in dealing with yours.