My car coolant is mixing in with my engine oil creating a milky looking oil. So I was wondering should I just change my head gasket? Plus my exhaust throwing out white smoke.

All related to a blown head gasket or a cracked head most definitely.

You would have to have the head checked for cracks, and reworked before putting it back on. But if there is a lot of miles on the engine, it would not be worth it to do..

Rowefast my car only has 127,458 miles

I had a good mechanic tell me that once the coolant and oil mix it gets circulated all through the engine and only a complete tear down will do , but of course people do replace head gaskets all the time and drive without a problem . So , what ever .

It depends on how long the engine is ran and the condition of it prior to mixing and of course the worst is to let it sit without draining water and changing oil and turning it over to cover internals without any coolant added first otherwise the oil/water separate and with temp changes condensates on the parts above and starts to rust. Then its a boat anchor.

If water mixes with oil you correct the problem, change the oil, then a good long drive will take care of the rest. It will be turned to steam and consumed by the engine via the pvc. If you have left the problem for a long time it will start to lose oil pressure and the lifters and hydrolic tensioners will not work properly and will lead to a catastrophic falure.