There are some nice sites along the river. There is one that is shaped like a half moon. If you look at Recreation.gov site, they have photos of the sites. They also show which ones have 50 amp vs 30 amp.
You enter the park via a small town (forgot the name) and the campground is just inside the park gates. There is an on/off shuttle system that actually has a couple of stops in the little town. There are some nice restaurants and shops.
I don;t know your physical condition, but the last stop on the shuttle leads to a famous river walk. The river meanders through some beautiful tight canyons where you may walk 300 yards along the shore and then 50' through the water. A lot of fun and beautiful....bring your camera. That time of the year, the water should still be warm and low.
Lastly, Bryce is also a beautiful park and is about an hour away. You can only get there by car. There is a limit on RV's. I can't remember the name, but there is a another park, just at the north end of Zion that is all part of that system. It's about an hour farther north on the I-15. If you can, you should take day trips to both parks.
Here is just one photo of the river walk. Where shorts and tennis shoes that you don't mind getting wet. There is a place in town that rents water shoes, walking sticks and dry suits. We rented them because we were there in April, but they weren't really needed.