Other unrestricted draw spells that I think merit at least consideration for some maindeck slots:
additional big-Jaces (though that's nearly a triviality given how good Jace is)
See Beyond
Preordain
Impulse
Probably the strongest for Oath aside from Jace is Preordain.
Or here's a slightly off the wall suggestion: Sylvan Library? Library prevents you from ever drawing a creature, and may be slightly better for filtering in Oath than Top due to the risk of having to use Orchard to pay for Top. Similarly Library is decent in theory against Shops since its effect occurs each turn without additional mana investment. If Library gets hit by a Nature's Claim that's one fewer that can be used on Oath, though its an unnecessarily juicy target for a Trygon Predator trigger.
I've given all these a shot, and/or played them in tournament within the past year.
Big Jace is the ideal card. It does a lot of things Oath wants to do like draw cards, put creatures into the library, answer threats like True Believer or Trygon, provide an alternate win condition in the case of SadSac, or circumvent our opponent's hate cards directed at the Oath. It just does a lot.
Preordain is also a very good card. I would highly recommend it to anyone playing Oath.
Impulse and See Beyond, and other cards like Night's Whisper or Scroll Rack, all suffer from the drawback of costing 2 mana. When we just want basic card manipulation, there is a world of difference between spending 2 vs. spending 1 (for Preordain). When we consider that the strength of an Oath deck is really in its ability to produce an early Oath in the first couple turns, and we can only expect to have about 3-5 total mana during that course of time, we really can't afford to be wasteful with our mana. I feel that Preordain is superior not because of what it provides when we cast it, but because it demands less from us when we want to cast it.
Top is a card that I have enjoyed for a while, even in Oath, though it does suffer a few key drawbacks. First, it is not blue and Oath decks tend to be hungry for blue cards to support Force. Second, there is the aforementioned problem where we might be forced to tap our Orchard in order to use the Top itself. The third problem is that it doesn't really play too well with Jace. What I mean is that if we have a Jace and a Top, sure we have a Jace, but we don't need the permanent selection and utility of the Top anymore. It seems better to do something like Preordain into Jace, or Jace and then cast Preordain, whereas Top is basically a total blank once Jace lands.
Sylvan Library is an interesting card. Being green, costing 2 for card manipulation, and not having an immediate impact were drawbacks. They could be worked around if the card was strong enough though. But the real deal breaker, at least for me, was the life loss. It's really tough to nuke our life total at 4 life per card when we're giving our opponent spirit tokens. It doesn't help that Sylvan lends itself to passing the turn a bit, like even if we use Sylvan to find Oath that's at least 2 attack phases for our opponent before we get to trigger the Oath.