Hi Chai Lover,
I've had my ileostomy for 28 years and in all that tie I had wafers with precut holes, but that changed since my stoma shrunk over the years; and my stoma nurse changed me to bags I have to cut myself.
It took me a few months to figure out how to make a template of my stoma.
I use curved ostomy scissors to cut it. And I use the stoma hole guides which either come with your bags and wafer or your one piece bag - of it does not ask your stoma nurse for some!!
Because my stoma is oval in shape I need to use three different hole guides to make the template, which I make out of cardboard, but every once in a while I need to remake it as the cardboard alters in shape - perhaps I need to find a better paper or plastic.
I mark the areas where my stoma no longer fits, (if that makes sense?) - and I write on the guide if it is the top, bottom, left and right side, than I first draw it on some paper, cut it out and hold it over my stoma to see if it is a good fit. My stoma nurse says to give my stoma 2 to 3mm of room so that when it contracts it's okay.
There are quite a lot of YouTube videos also which show you how to do this - put a lot involved using a piece of plastic which you put over your stoma and mar the edges, but that didn't work for me as the end result was always too big.
All the best,
Gracie