I have never found a pair of traditional hiking boots that was really comfortable on me, and I have tried on literally every shoe in REI and the local outdoors outfitters, plus ordered and returned dozens (literally) of pairs of boots from L.L. Bean, Zappos, etc. I am the boot-fitter's despair.
But the good news is, you don't have to wear boots to hike! I hiked 100 miles in 9 days in lightweight Merrell low-tops. They are hiking shoes but only a little stiffer than a running shoe. On that hike I ran into plenty of people who were wearing sneakers, and plenty who were wearing heavy leather boots. It's a matter of preference. When I visited Zion I wore only barefoot-style trail-running shoes. If you are comfortable walking the kinds of distances you will be hiking in your current sneakers, I wouldn't worry too much about it.
If you do the Narrows hike (HIGHLY RECOMMENDED!) you will want to wear water shoes of some kind, or sneakers with plenty of mesh will work too (you can rent special water boots for the Narrows).
Oh and, Zion in summer is hot (cooler than a lot of places in Southern Utah, but still hot). I wouldn't want to be wearing boots and wool socks.