Veritas has a perfect solution for Office 365 - Veritas SaaS backup.
No integration with BE - it's a separate cloud-based product.
No onsite infrastructure is needed (no server, no storage).
Licensing is per user, subscription based, and standard retention is one year. Additional retention license can be added.
Product page with link to 30-day trial over here: https://www.veritas.com/product/backup-and-recovery/saas-backup
Hope this helps.