IMO, the number one priority for the Bears is the development of Fields at QB.
Jim Harbaugh, despite having some of the top QB recruits in the nation since 2015, has failed to develop a good QB at Michigan.
My choices for HC would be any one of Greg Roman, Kellen Moore and Byron Leftwich.
Roman not only transformed the Ravens offense (in mid season no less) to Lamar Jackson's skill set, but also did the same with the 49ers and Kaepernick years earlier.
Moore is a coach's son who was calling his own plays at age 16 in H.S. He's helped develop Prescott and make Dallas a top notch offense. Reminds me of Sean McVay.
Leftwich has been Arians' right hand man for a while. If his offensive/QB philosophy is the same - I'm assuming it is - then he'll be a solid HC.
Also, I would see what it would take to nab Jarod Mayo from the Pats staff to be the DC. Give him an Assistant HC/DC title and offer him more money and maybe he comes?
The combo of these two would cost less than just Harbaugh alone and would put us on a better path IMO.