Ah, okay. Your situation clarifies a little better what you meant. I think your card is not worded correctly--it would actually be a kind of card we haven't seen before, I think. Is this wording more what you mean?
Attic
Cost: 3 coins
Type: Action
Effect: Discard any number of cards, then draw that many. (This card takes 0 actions to play).
It's slightly interesting that you could play it after a draw card like Smithy or Council Room, but the fact that you'd still be out of actions and couldn't play any more actions is a big negative to that particular benefit (you could still play more Attics, I suppose, but you wouldn't be able to play other Actions). To mitigate that, you could make it something like this, but it would be a fair amount stronger:
Attic
Cost: 3 coins
Type: Action
Effect: +1 Action. Discard any number of cards, then draw that many. (This card takes 0 actions to play).