Texas and Oklahoma are leaving the Big 12 for the SEC. While people are talking, it is not likely that the likes of Texas Tech, Iowa State and Kansas State are going to be attractive to other power conference, while Oklahoma State and Kansas are. Therefore, the Big 12 needs to immediately step up and make moves to keep OSU and KU in the conference. Therefore, here is my suggestion.
Houston
The program is in the largest city in Texas and in the metro area that has added the most people in the 2010s. Surely, there is enough people in the Houston metro to add the Cougars.
Boise State
Sure, you won't see the Sooners on the Blue Turf anytime soon. But this will be a fun add. Boise is not a big city now, but it will be soon. Possibly by the end of the decade.
Brigham Young
If any school deserves to be in a Big Conference it is BYU. If you don't like Sunday play, then add the Cougars as a football-only program. There other athletics programs are already in a good conference.
Air Force, Army and Navy.
The three service academies deserve to be in a bigger conference. Army and Navy will be good travel partners for West Virginia. It will help the schedule for these schools to be in the same conference.