How long does it take you to perform the full backups currently?

What is your allowable data loss in the event of a server down?

How many backups do you intend to keep?

If you elect to do a differential backup, you would need to keep your most recent full backup and most recent differential.

Correct, in simple recovery you do not need to perform transaction log backups. If the data loss potential is acceptable for that, then you are fine. However, if data loss of a day is not acceptable, you should consider changing to full recovery model and backup your tran logs.