Use a resistor to bypass the airbag. That's all an airbag simulator is. Use the stock seat rails. Done.
For seat covers, most are made for cars with seat airbags, if not cut a slit in them. Myself I wouldn't care, if you're in an accident bad enough for the bags to go off the functionality of side airbag will likely be the least of your worries.
View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)