Hi @[deleted],
There are various controllers out there, the first thing to think about is how many pedals/buttons you need. I suspect you will only need a handful for simple switching between groups.
Would it be handy if the controller was wireless? The Blueboard is particularly popular, it's bluetooth and can run on batteries. Only 4 pedals though, you can switch banks but from my experience, having all your controls quickly accessible is a must.
If you want something bigger then the Behringer FCB1010 is a good option. Lots of pedals but you have to plug it in to the iPad via a midi interface and camera connection kit. It can be a bit of a faff.
They are the two I know of, I'm sure there are some better options out there. The main thing is that it works with IOS. The other is the number of pedals. Bluetooth MIDI can make your setup a lot simpler as well, invaluable for live shows.