I have he same issue. I have a loop Ileostomy. I wear a Hollister "Red" 1-1/4 Precut Convex Wafer, and High Output Pouch. I have experimented with Convatec and Coloplast. Whenever I tried using the Convatec of or Coloplast wafer, I noticed that the area around my stoma would feel itchy. Upon removing the wafer, my skin would be red and swollen. The Coloplast wafer would actually cause my skin to bleed and weep. I had to switch back to Hollister. The Holister works well for me.
The only issue I have is that I don't really need a two piece system. I like the simplicity and less bulk of the one piece. I wish Hollister made a One Piece Convex in the High Output Pouch. I have had good results with the Nu-Hope One Piece Convex High Output. Nu-Hope makes their stuff custom to what you need. You can call them, and they will make whatever you need. You can then order it from Edgepark.
I currently switch between the Hollister and Nu-Hope. It feels good for me to alternate because the pressure points of the convex wafer are in different areas for each brand. It gives my skin a break between changes. Hope you find something that works.