Normally you have a base animation that handles idle/movement (Just add the dodge roll to that).
Then on top of it you have 1 slot for upper body that is generally independent because it is activated via montage rather then state machine.
The player character does trigger animations directly as they are nothing but a result of a button press - so even if in AnimBP they are factually still a deferred call generating directly off player input or the character class.
You can definitely create an upper body relative state machine and use it, but it overlays to the motion state machine so just create an attack idle state and transition to it. Its just a copy, but specific to any attack you trigger.
That way if you are idling you can keep the bored idle animation as it is, the transition between attack and idle will be mirrored by the fake idle state for the attack.
You should do the same for movement too.