Advice needed : BMW e60 2010 rwd 353i

[N0Bl1nker]

Hello , i bought the car two weeks ago , and i just got the check engine light on .

The car smokes from exhaust on cold start white smoke and smell like gas and after it gets warm when i drive it stops smoking .

I check with the computer and it shows the code 29E1 DME mixture Control 2 : ECM (Engine Control Module - DME/DDE )

https://bimmers.com/blog/29e1-bmw-co...-does-it-mean/

I checked with a mechanic and he first said it must be head gasket because the coolant was low when he checked and he first doubt that the coolant was going on the engine and thats why the smoke its going out but after he ran the computer i guess he saw the same code " rich " on the o2 sensor i think and then he said it might be injector and he suggested to change the ones on first bank 3 of them for 1200 dollars.

Do u guys experienced this before and what do u suggest?
And what injector do u guys suggest to go bosch or index12 to go with ?

I just want to make sure im on the right path or what other diagnostic should i do before changing anything

pls need help thanx