Depending on the width of your wheels, 215's should work fine.
Also, per the TireRack's spec for Michelin Engery MXV4+ tires:
If your SRS light comes on a long-straight highway driving, 98% it's the steering-wheel's slip-ring and brushes. My 1988 W124 wagon had the same symptoms, and the slip-ring was worn-thru and lots of brush material.
A very CHEAP fix (parts under $70) takes about 30-45 mins.
You do need some long-handled allen tools and you have to discharge the airbag system by disconnecting the RED connector in the passenger foot-well (I would disconnect the battery ground as well afterwards).
Have fun with that 5-speed!