[gyrfalcon]

What exactly you get equipment-wise between the two sport packages depends on the model you get.

Your main questions though are easy. There are no difference in the seats or suspensions between the sport and M sport packages.

As for the wheels, you can't get 17in wheels on a 135i with any sport package unless you buy them aftermarket. Both 128i sport packages come with 17in wheels though.

Now as for the specifics what you in addition to the non-M sport packages.
128i M sport pack adds different 17in wheels, black anthracite instead of grey headliner, thicker M steering wheel, 135i style front bumper, 135i style rear bumper with diffuser, and M shift knob. Maybe a M dead pedal too but not sure.
135i M sport pack only adds the headliner, and different 18in wheels.

Also M sport packs are only available on certain exterior colors.