My Berghaus Freeflow rucksack seems to be on its last legs, so it looks like I'll need a new one for commuting. What I like about the Freeflow is that it has a back system that keeps the sack clear of your back, so there's less of the sweaty back syndrome. What I don't like is the zips which have broken on it, which after five years of fairly light use is disappointing. Any replacement will need to have some back support which allows air to get the back (I'm rediscovering the joys of sweaty back syndrome!) and be durable, preferably not using zips to close the main compartment. Any suggestions?