I feel like it's a little sad to just make the fighter more like the barbarian, in order compensate for barbarian currently being very powerful - according to what some people have been telling me.
With that said, it might be the correct path to take since I can't come up with other things than DI, perhaps DR but that is also a very powerful thing and both things seem to be more barbarian, than fighter-specific. With fighter's identity being based on feats, perhaps it just needs some fighter-only feats available that grant the things you suggest, or perhaps feats that grant more AC. Even though it ironically is already pretty feat starved, with some feats being a must like weapon specialization and cleave.
Fighter has two things that barbarians don't - feats and access to heavy armor. Perhaps it is also time to make some more powerful heavy armor available making them only useable by fighters.
With that said, it might be the correct path to take since I can't come up with other things than DI, perhaps DR but that is also a very powerful thing and both things seem to be more barbarian, than fighter-specific. With fighter's identity being based on feats, perhaps it just needs some fighter-only feats available that grant the things you suggest, or perhaps feats that grant more AC. Even though it ironically is already pretty feat starved, with some feats being a must like weapon specialization and cleave.
Fighter has two things that barbarians don't - feats and access to heavy armor. Perhaps it is also time to make some more powerful heavy armor available making them only useable by fighters.