If your transaction logs are getting big even in SIMPLE Recovery Mode, could it possibly be that you have a great deal of DML occuring without commits? INSERTs, UPDATEs and DELETEs for example. If so then performing commits after a certain amount of DML activity could help.

Just out of curiosity.....how were you planning to do Transaction Log backups while the database is running in the SIMPLE Recovery Model?

The transaction log stills plays a part in a database running in the simple recovery model. Why? Because even in this model it is still possible to rollback uncommitted transactions and these transaction are stored in the transaction log until the commit occurs. Once they are committed they are no longer in the log. Hence the reason I wrote the first paragraph.....

And please learn how the transaction log and recovery models work......