M4A/AAC/MP4 can be lossless.
Where are you listening to your music from? Chances are that unless you are playing it through some super top of the line headphones or amp/speaker setup, you will notice little to no difference between lossless and M4A @ 256kbps or better. I prefer to keep most of my CDs and LPs archived in the lossless AAC format (a.k.a. ALAC, or Apple Lossless Audio Codec), but on my iPod I have it all in 256kbps AAC to use less HD space and not use as much battery life.