Is it good idea to change Simple Recover Model into Bulk-Logged on ETL system?
Bulk Logged will not help you in this situation.  Your transaction log is growing because you are performing large transactions.  In simple mode, the log is truncated after a checkpoint.  

Depending on how you are loading your data, you may need to break it up into smaller chunks.  Make sure you are not loading all the data in one large transaction.