Armour class seems a pretty uninmportant stat at the moment - I'd also suggest you reverse the way it works in order to make combat more interesting.
As you probably know, the higher your armor class the harder you are to hit. At the moment armour class is increased by wearing armour. The heavier the armour the better the AC.
I suggest armour class is instead highest when you are unarmoured, and is decreased by wearing heavier armour. Maybe AC starts at 50, maybe higher maybe lower. It would have to be tested.
Leather jackets will only reduce your AC by 5. They barely restrict mobility.
Leather armour reduces your AC by 15.
Metal armour reduces your AC by 30, and so on.
That way heavier armour has setbacks - wearing combat armour will make you a lot easier to hit, but it obviously provides better protection.