Which engine? What year?
Yes, this makes a difference because the 4 cylinder engine uses a compressor that cycles on and off like it does on most cars. The V6 uses a compressor that is on all the time when the A/C or defrost is on (modulates internally).
Personally, I do not trust and compressor seals past a certain age, irregardless of mileage.
Look here, it's really all you need, if you have the V6 (will work on the 4 cylinder engine as well):
http://www.aleromod.com/forums/showthread.php?t=34167
Adding r143a is easier than an oil change. Probably at the difficulty level of changing the air filter.
I bet you have a leak and are just low of r134a. Amazon sells 12 packs of 12oz cans cheap enough:
http://www.amazon.com/Johnsens-6312-...dp/B00C873Y60/
Buy some now before it gets hot. The price only goes up from here until next winter.
I put at least 2 cans of these in my Alero last summer. If I could find the leak I would fix it, but can not even with an electronic detector and various dye packs.