Writing down your comments; in our case it is not so critic and a backup every 3 hours is just OK: 3 servers and about 100+ users, but due to the nature of the applications the amount of transactions isn't particularly high (moreover comparing to your situations). Anyway a complete data backup is taken every night an this is replicated to tapes.
What is important for me, and what I will change is the way we're working with transaction logs, following your advice.
Thank you very much for your kind help, and keep seeing you around 🙂
Best regards,
Okiwan