I tried Sprengers and found the sideways flexing a bit weird.
I have endurance stirrups ( effectively a lump of sponge under the foot) on my western saddle so I looked for similar.
The ones I bought are Compositi reflex stirrups which cost £20.99 from Decathlon.
Everyone who has tried them as remarked how comfy they are as the footplate flexes but the sides don't.
Just snapped a photo with a pound coin for scale - these are 4 3/4" wide.
(
Please excuse the dust as this saddle hasn't been used for a couple of months.)