I am also a big bellied guy, and I have the same problem. I like the Kydex holster, but it rubs my side raw. I decided to wear it one night, since I was going to the ATM at 2 o'clock in the morning. as well as grocery shopping after I left the ATM. By the time I got home, my left side (I'm left handed) was rubbed so raw that it was on the verge of bleeding....and that was only after wearing it for a few hours.(I was carrying my Sigsauer P938, 9mm handgun.) I tried a leather holster, but being fat, it smashed the holster, making it difficult to draw the gun or to put it back in the holster. I need to carry a gun inside the waistband, since I can't tolerate the heat of summer, so I can't wear, long baggy shirts to cover an outside the waistband holster during the summer.
I saw one comment that said to go on a diet and exercise...that only works if you are young. When you are old like me, that doesn't work. I pedal a stationary exercise bike every day for 60 minutes, and if anyone else ate the amount of food that I eat every day, they would starve. (3 hard boiled eggs for breakfast, and a tossed salad for dinner, yet I weigh 295 pounds for some stupid reason..) I have a concealed carry permit, but I can't carry because of the holster problem. I can't get a pocket handgun, because my pockets are always filled with stuff that I use every day. It seems that my only solution is to get large, baggy shirts, cut off the long sleeves, and wear them all year long, including the hot summer months, and just sweat to death.