Replacing Unarmored Defense

[Kendrik]

So I am going to DM a campaign soon with two players. It’s going have almost no magic. The party will have generally low resources (They will start the campaign with no possessions besides a bronze dagger each and some rags to ware) and good armors will especially be a luxury. However, one of the players is playing a barbarian and recently pointed out to me that Unarmored Defense will basically negate my “low armor low ac” plan for the campaign. He offered to just ignore the power but I want to give him something to replace it with.
Any suggestions?
I’ve considered just giving him a fighting style but I would like to know if anyone on here might have a better suggestion on what to replace it with.

[MrStabby]

Maybe proficiency in dex saves? It is another defensive feature, it probably won't make them the best in the party with this and is moderately powerful.