When I went back to driving, I put a small pillow between the seat belt & my chest. Prior ro that, the longest ride I had was about 60 minutes, between Dallas & Fort Worth TX.
About 2-3 weeks after John's MV repair, we took a weekend trip about 2 hours south of our house. He had a surgical complication (very minor) of lymphedema, which caused some swelling in his left leg. So we had to stop a few times during that 2-hour drive both ways so he could walk around. He sat in the back seat and propped his leg up. No way to tell how he would have been on the ride w/out the lymphedema.
I would definitely sit in the back seat for the first 4-6 weeks post-op. You do not want to have an airbag going off, causing deceleration trauma and fracturing your sternum, at the least, or injuring your heart, at the worst. If it's going to happen, let it do so once you're totally healed.