Sure you want a rack bag?
there are some decent rack bags out there, but the main issue i have with them all is that they transfer lots of road shock to your compy. With it on your back you’re filtering nearly all of that out, plus it’s out of the rain and out of the way of wheel spray when it is wet. if it’s just the fact that the bag is uncomfortable that’s bugging you, why not invest in a really nice laptop courier bag? get one with a proper semi-rigid padded sleeve, and make sure the bag has a sternum strap to keep it well behaved when you’re cycling. crumpler bags are good, so are knog ones.