In reply to girlymonkey:
What bag do you have at the moment?
you say it digs in. does it have Aluminium bars for support? if so these can be shaped to fit better maybe.
sizes are just a gauge, each manufacturer measures up differently, when buying a new sack its a good idea to go in with what you expect to carry and pack it to check it all fits in, plus you then have the benefit of trying it on with your usual load to check comfort. shoulder straps and hipbelts all vary, if you are slight of frame then POD may not suit,
Best bet go shopping, open mind, try them out, if nothing local, go a bit further afield
HTH