Yeah definitely don't go cheap on brakes. For the pedal issue, it's 90% likely just your fluid issue... it's an 05, don't think there will be any problems with your brake lines yet, possibly master cylinder but to diagnose that might as well just do a full fluid flush and while there upgrade to dot4. As for the pads and rotors, since you're going to be taking off the wheels to bleed the brakes might as well replace those too, go with good stuff... also if you don't know how to do it yourself, take it to the shop, you'll pay arm and a leg but atleast it will get done right.
2010 Cobalt SS: Full Bolt-Ons, tuned. -- Sold.
2014 WW Evo GSR: S/S & Interior Package