It could be tricky. Apple disable TRIM in OS X where a non-Apple-approved SSD is detected. The drives Apple use (far as I know) are the Samsung 830 and some Toshiba drive. If you could get one, OS X should hopefully enable TRIM for it. But the 830s aren't sold retail any more (and if they're not manufactured, maybe Apple are using the 840 now?). I hate to say it but it might be best to just take it to Apple for an upgrade and get a bit ripped off.