My car has been consuming oil a lot

I have a 2002 Nissan Altima and my car was doing the same thing. I have replaced the catalytic converter and had a hairline crack in the manifold repaired. Now I have blueish white smoke coming out of my tailpipe and smoke coming from my engine. There is exhaust coming through my vents when I have the defrost on and the car shakes really hard when I come to a complete stop. I recently found out that my head is gone in my engine and front catalytic converter and manifold need to be replaced. I am debating now whether I should just replace the entire engine or just the catalytic conver, manifold and the head. After reading the many horror stories about this car you should replace the catalytic converter now before you blow your engine because it is sure to happen. The exhaust from my tailpipe is vacuuming into my engine, when I put my hand to the tailpipe you can feel the suction. This is a common issue with this car and Nissan knows about it. They say there was a defect in the catalytic converter upon manufacturing and it is not under warrantee now. Good luck