If I have Soraka and Baited Hook and a 3 might unit and I Baited Hook my 3 might unit and they're all in base, do I get to use Baited Hook ability and keep my 3 might unit?

Yes, you keep your 3 Might unit, but you do not get to use the full effect of Baited Hook.

Because Soraka, Wanderer is at the same location as your 3 Might unit and has higher Might, her replacement ability intercedes when Baited Hook attempts to "Kill" your unit. As a result, the unit is saved and is not sent to the trash. Since it was never killed, Baited Hook fails to reference a "killed unit" for its secondary effect.

Sequence of Events

1. Activation: You activate Baited Hook, paying its costs and targeting your 3 Might unit at your base.
2. Resolution (Closed State): Baited Hook begins to resolve.
3. Replacement: Soraka’s replacement effect intercedes before the "Kill" game action occurs. Instead of being sent to the trash, your 3 Might unit is healed, exhausted, and recalled to your base (per Rule 369 and FAQ #9379/1171).
4. Effect Failure: Because the unit was not killed (it did not go from the board/base to the trash, per Rule 415.2), there is no "killed unit" for Baited Hook to reference.
5. Partial Resolution: According to Rule 359.3.e.12 and FAQ #10387, the check for the "killed unit's" might returns "null." Consequently, while you still perform the instruction to look at the top 5 cards of your main deck, you cannot satisfy the requirement to play a unit with "Might up to 1 more than the killed unit."
6. Cleanup: You recycle all 5 cards looked at.

Summary: Your original 3 Might unit remains in your base in an exhausted state, but you are unable to play a new unit from your deck using Baited Hook.

Note: I could not fully verify this ruling against the retrieved rules, specifically regarding the Might value of Soraka.